Skip to content

Keeping Koi Carp

Koi carp are a beautiful fish to keep in a pond, due to their bright colours and interesting patterns. Koi grow quite large and will just continue to grow, as opposed to other pond fish which generally grow to fit their surroundings. For this reason, it is vital that you have a large enough pond for the Koi to roam around, particularly if you have a number of fish. Koi will happily mix with other pond fish; however, they do need a little more care and attention put into their surroundings. Koi will eat pond base and plants so choose either heavy duty plants or keep pond plants to a minimum. Ensure pond water is continually fresh, and if possible, use a pond filter. Although Koi are fairly strong, they are inbred, which makes them slightly less sturdy than some other pond fish. Try not to feed them in too cold weather as they find this traumatic. With Japan being their country of origin, they are used to short winters but can struggle in longer periods of cold weather. Try to make the winter months as comfortable as possible by shielding the pond from strong winds or using a pond cover. Choose high quality Koi pet food and not just standard pond food. Floating sticks with high protein content are best as these promote healthy growth. Food which contains Spirulina is highly effective in maintaining the bright colours in the Koi.

What Determines the Price of a Koi Specimen?

Koi are rewarding fish to keep, and many people take great pleasure from theirs. If you are considering setting up a koi pond, then you will have to invest in stock. There is a fabulous array of fish to choose from. There are more than 20 different types, and these are defined by their colour, patterns and size. With some fish costing only a few pounds and other specimens selling for thousands, how is the value of a koi carp determined? Getting to grips with the factors that influence the value of koi will help you to decide which fish are best for you. It really helps if you know how much you should be paying if you want to ensure that you get the best value for your hard-earned cash. Koi pricing can seem confusing and there are no hard and fast rules. You may also find regional variations in pricing so it could pay to shop around.


Many fish are commercially bred in large numbers with little attention paid to selective breeding. On the other hand, koi breeding is a very serious matter for some people who selectively breed to produce various traits in their fish. These breeders may also be dedicated to developing specific bloodlines. Just as with cats and dogs, top specimens from sought after bloodlines will cost a great deal more than a random fish from a pet store.

Size Matters

The cheapest koi will often be small specimens. They will require careful nurturing in order to grow. Larger koi have been cared for over a long period of time and will command higher prices.

Age Matters

Larger koi will be more mature but there is a point at which that maturity will reduce the value of the fish due to the more limited potential lifespan of the specimen. However, koi can live up to 50 years and so a fish has to reach a comparatively venerable age before its value is impacted.


colour and pattern distribution of a koi is considered to be one of the most important factors in determining its desirability. A Koi with a desirable colour and pattern distribution will attract a higher price. The most sought-after and, therefore, the most highly valued Koi pattern is a design that is reminiscent of the Japanese flag. This is a white fish, with one lone red spot on the back of the head. Koi exhibiting this colouration and pattern are extremely rare.


Of the 22 recognised types of Koi, some are more in demand than others. If your budget is tight then you will still be able to invest in fish of a significant size but may have to avoid the more sought after types. Only you can decide what you should spend on your koi. It could be that you care little about the specific colours, patterns and bloodlines and so could find some great specimens at favourable prices. But if you are seeking fish from recognised bloodlines or of a certain type then you might need considerably deeper pockets

Is Koi Keeping an Expensive Hobby?

If you are attracted to the idea of keeping koi, you must consider the financial implications of your potential new hobby. Koi can live for 30 years and more! The costs will depend on the scale of the pond that you create, the construction method and whether or not you build it yourself. But a koi pond is never going to be cheap!

Complex Needs

If your idea of a constructing a pond is to dig a hole and to throw in some pond liner in, then think again. Koi would not survive in this type of garden pond. Koi need a generously proportioned pond with exceptionally clean water in order to thrive. In other words, you need a big pond and some serious filtration equipment. There is no hard and fast rule when it comes to pond size, but your pond will need to have a volume in excess of 4,000 litres. 7.5 metres long by 4 metres wide is probably the optimal size and that means that you face a serious and expensive project to create your pond. It will cost you at least £15,000 for a professionally installed fibreglass pond with heaters and filters. But you could easily spend more if you have extravagant plans. Unheated ponds are cheaper to install and to run but are still going to set you back a considerable sum, especially if you have to engage a contractor to do the work.

The Ongoing Costs of Koi Keeping

You will face ongoing costs too. Your water bills are likely to rise considerably if your supply is metered and those pumps, filters and heaters will increase your energy bills. You will also have to finance food and water treatments. The cost of food will depend on how many fish you keep. As a rough guide, 15 koi will cost around £100 per year to feed.

How Much do Koi Cost?

The cost of your stock will actually prove to be the least of your problems unless you insist on investing in prize specimens and that wouldn't be a good idea if you are just starting out. You will be able to buy fish for as little as £10 but premium koi can cost thousands. You should also think about what will happen to your fish if you are away for more than a few days. Do you have friends and family who would be prepared to look after them? If you don't, you will incur more expense paying someone to take care of them. It is also worth thinking about how long you will be living at your current home. There is no point attempting to finance an expensive pond installation if you might be moving in the next few years. if a move is on the cards, try to choose a set-up which enables you to maximise what you can take with you when you move. Investigate all of your options before making your decisions and choose a pond which you can afford to build without seriously impacting your lifestyle.

What is the best size for a koi pond?

Are you thinking about featuring a koi pond in your garden? Perhaps you already have a pond but are concerned that it might not be the optimum size. There are several reasons why size really matters!

Don’t overstock your pond

You may be challenged for space and your budget might restrict the size of pond that you can build. But it important to remember that koi do not do well in overcrowded ponds. If there are too many fish, they can’t engage in their favourite hobby – swimming around. In addition, there won’t be enough secluded areas of the pond for all of the fish to retreat too when they feel the need.

Maintain good water quality

To make matters worse, an overstocked pond will make maintaining good water quality next to impossible. There will be too much fish waste in the water causing ammonia and nitrite to develop and your fish will most likely succumb to serious health issues as a result.

Small ponds and temperature change

The smaller the volume of water, the greater the speed at which it heats up or cools down. Koi do not react well to rapid temperature changes and so are better suited to larger ponds. Shallow ponds are particularly prone to rapid temperature changes.

Your fish will grow

What appears to be an understocked pond could soon start to look overcrowded as koi can grow very quickly. You should bear this fact in mind when stocking your pond and err on the side of caution. Fortune rarely favours the brave with koi ponds!

It is best to think ahead and plan carefully because choosing a smaller pond could prove to be a false economy as you may end up having to build a second pond or a much larger replacement to accommodate your fish. What appears to be a huge pond at the outset could start to look rather diminutive when your fish have had a few years to grow.

What size should you choose?

If you are a beginner, it can be hard to decide what size of pond to build. Start by thinking about how many fish you would like to keep in it. A good rule of thumb to work by is that you should have 10 gallons of water for every inch of fish and a minimum of 1000 gallons in the pond. Your pond should be at least 3ft deep. In addition to helping create a more stable environment, a good depth of water helps your Koi to exercise. Swimming up and down causes their muscles to develop and results in a good, streamlined shape to their body. Koi that have been kept in shallow ponds often develop a somewhat obese appearance like a rugby ball! A pond which is 3ft deep and which measure 8ft x 6ft would contain a little over 1000 gallons of water but this size of pond could only safely accommodate 5 koi. You are going to need a significant amount of space to create the perfect pond!

Koi Pond Filtration

When you have settled on the position and size of your Koi pond, the next step is to ensure that you have a system that provides excellent filtration. It is essential that your pond provides a healthy environment for your stock and filtration is key; get this wrong and you may find yourself in deep water (not literally).

Waste removal

Your stock of Koi Carp will produce large amounts of waste. Basically, your pond is a giant latrine for your fish and so filtration is required. Your filtration system should include good mechanical filtration to remove solids from the water. Different types of mechanical filter are available. These are various in type and employ nylon brushes, plastic media or a vortex to trap solids. You should choose a filter that is easy to clean. A good quality gravity filter will have an integral drain so that it's easy to flush waste away. The filter should have a valve to shut it off from the pond so that you can clean it regularly.

Biological pond filtration

Your pond will also require biological filtration. A biological filter uses friendly bacteria to break down ammonia in the water. Ammonia is an inevitable consequence of your Koi's metabolisms. The friendly bacteria live on the filter media. The ammonia is broken down into Nitrite and then to relatively harmless Nitrate. You must control the level of nitrate in the pond by regular small water changes. It can take five to six weeks for friendly filter bacteria to build up on your filter media. During this time it is best to introduce only a small number of fish to your pond. It could take several months for the bacteria to mature fully and so only then will it be safe to fully stock the pond. Do ensure that you choose a big enough filter. Bigger is better and could be cheaper in the long run. Buying bigger might mean that you won't have to invest in another filter further down the line, when your fish have grown in size or you have increased the number in your stock. Your Koi's health is reliant on your filter so initially prioritise the quality of your filter rather than the number of fish that you invest in.

UV Clarifiers

Clear water doesn't necessarily mean healthy water but of course it's nice to be able to admire your fish. UV clarifiers eliminate green water and are available as standalone units, although many biological filters incorporate a UV filter. Water is pumped through the clarifier where it is exposed to high levels of UV light. This causes single cell algae in the water to clump together so that they can be collected and broken down.

Feeding Your Filters

You can feed water to your filters either with a pump or by a drain in the bottom of the pond. Many successful modern Koi ponds use the latter. This is called a gravity fed filter system and is beneficial as it delivers solid waste to the filter intact and so it easily settles and is simple to remove. Gravity fed filters are the best choice for larger ponds, but you may require specialist help to install one.


Your filter system must be powered by a good pump. This should be capable of circulating the entire volume of water in your pond through the filter in no more than two hours. This turnover of water will ensure that ammonia is broken down at least as quickly as it produced. You should also pay attention to the running costs of your pump. A more costly but power efficient pump will save you money in the long run as pumps can consume a great deal of electricity.

Biological Pond Filters: Top Tips

Your Koi's health will be largely dependent on the efficiency of your pond's filtration system. Your biological filter utilises bacteria to break down the harmful ammonia in the water and converts it into benign Nitrate. Whatever your budget when setting up a new pond, filtration is a priority and you should invest in the best pond filters that you can afford at the time, even if that means reducing the number of fish that you plan to purchase at the outset. You cannot over filter your pond and so bigger is best when it comes to biological filters. Choosing the right equipment is essential but this is only the beginning of the story as over time your filters will need to be operated correctly and be regularly maintained.

Running Your Pond Filters

It's important that your biological filter must run for twenty-four hours every day - especially between March and October when your Koi will be most active and feeding. Going into more detail, ensure that you have a pump that is capable of turning over the volume of water in your pond at least every two hours. It's key that the water pass through the biological pond filter as you will want to match the rate at which ammonia is being produced by your fish stock. You should regularly check your pump's pre-filter to ensure that the correct water flow is maintained. When you install your pond filter it will take six weeks for the friendly bacteria to mature and several months before they fully mature. Do not stock your pond too quickly as you will have inadequate filtration. Clear water does not mean healthy water and so you should test your water quality regularly. You cannot tell if all is well simply by looking at your pond water. Test your water immediately if your Koi show signs of lethargy. You can kickstart your biological filter and then improve its performance by using a bacterial supplement.

Filter Maintenance

Always clean filter material in pond water and not in tap water. Tap water contains chlorine that will kill your beneficial bacteria. Only clean your media if your water flow is inhibited. Clean your media only when completely necessary and always follow the manufacturer's instructions. Use pond water and do not clean the media in one go. If you stagger your cleaning, you will maintain a healthy population of bacteria. Bacterial supplements can be particularly beneficial after you have cleaned the filter media and will promote rapid growth of friendly bacteria. If you have a UV clarifier, always isolate the power supply before starting any work on the equipment. Never look directly at a UV bulb and follow the manufacturer's instructions carefully. The UV bulb will need replacing approximately every six months. When you have to replace the bulb, change the O rings and seals at the same time. Handle the Quartz sleeve carefully and remove any dirt as required.

How to Control Algae in Your Pond

The pond environment is a complex one and can require careful maintenance to remain healthy, especially when a pond is new. A build-up of algae is unsightly and is detrimental to your fish stocks, also preventing you from seeing them. Fortunately, there is much you can do to prevent algae from forming and to rid your pond of this unsightly green film.

What causes algae?

Algae need sunlight, ammonia and oxygen in order to prosper. It's crucial that you're aware of the levels of ammonia, nitrite and nitrate in your pond and you can assess these using a testing kit. The test kit will give you a good idea of what is causing your algae problem if you have one. Alternatively, it will warn you when the conditions are ripe for algae growth.

Pond Pumps and Pond filters

Pumps and pond filters are vital for water quality. Your equipment must be suitable for the size of your pond and should be carefully maintained. Algae growth is often the result of poor filtration. This could be because the filter doesn't have sufficient capacity for your pond and so cannot process all of the waste material. The pond filter should be able to circulate all of the water every two hours. Your filter media contains nitrifying bacteria which break down ammonia. But the bacteria need time to mature. If your filter does have the correct capacity then any algae issues could be due to insufficient levels of bacteria in the filter. You can use cultures of bacteria to improve the situation. If your filter and bacteria are in order, then your problem could be due to overstocking. Removing some of the fish could do the trick. Your pump should be kept free of debris as this will impede your system. Clear your filter sponges of debris and then wash them in pond water. Do not use tap water as this can kill your good bacteria.


Algae could be prospering in your pond because sludge has accumulated at the bottom. This will be fish waste, uneaten food and decaying plant matter. The process of decay produces ammonia which again, promotes algae growth. Use a pond vacuum to clear the sludge and consider fitting a pond net to prevent leaves from falling into the water in autumn.


The fertilisers and other chemicals that you use in your garden often feature ammonia. Surface run off can cause this to end up in your pond water. Check the products you are using and then change them if necessary. The process of fertilisers causing water pollution and in turn encouraging growth in plant life such as algae is called eutrophication.

Excess Food

Uneaten food will eventually end up at the bottom of your pond where it will rot and release ammonia. Make sure that you are feeding the correct food for the species that you keep and feed only what the fish will consume in two minutes. Clear uneaten food from the water after this time.

The Sun

If your pond is exposed to the sun all year round then algae will prosper. You could consider relocating your pond to a more shaded area, planting large shrubs and trees to provide shade or even constructing a hanging garden.

Algae Treatments

Algae treatments are available in biological and chemical forms. This speeds up the breakdown of algae. You could also think about adding a UV clarifier to your filtration system. These shine UV light onto the water prior to it entering the filter. The process results in algae particles clumping together and being trapped in the filter where they are broken down. For a more natural approach, adjust your planting to feature ammonia feeding species. These will help to starve the algae.

Adding koi carp to your pond

Koi are very colourful and gracious creatures which make a great addition to your pond. It is incredibly relaxing to watch these beautiful fish swim through the water. Koi usually live for an average of 25 years; however it has been documented that some koi live to twice this age. In order for your koi to live a happy and healthy life they need the right environment and the right nutrition. Choosing koi carp, however, can be a very challenging and time-consuming exercise as they vary greatly in price due to country of origin and specific colourations. It is a good idea to do some research on the Internet to find more about different breeds.

It is also very important to remember that koi need lots of room to live so you must ensure that your pond is the right size. As a rule of thumb, a minimum of 1,000 gallons and 20 inches deep is recommended. If your pond is currently empty of fish, always make sure that your filter and pump have been running for a while as to ensure beneficial bacteria have had the time to establish themselves. These healthy bacteria are important for maintaining the right chemical balance in a fish pond.

It is always a good idea to view koi carp before you buy them. Koi should look healthy with clear eyes and healthy fins. Usually, smaller, younger koi are considerably less expensive than larger varieties. It is usually a good idea to make sure you do not buy too many koi in one go. This is due to the fact that if too many koi are added, the bacteria in your pond will not be able to handle all the fish waste. This could lead to health problems in your koi.

With regards to feeding koi, there are a few simple rules to follow. Firstly, in the Winter a koi carp’s metabolism considerably slows down and they become a lot less active, which reduces their need for food. When the temperature falls below 4°C you should not feed your fish at all. During the winter, when the temperature is between 4°C and 10°C, a good quality wheatgerm food should be used. When Spring arrives and the temperature is between 10°C and 18°C, a good quality staple food should be used which contains moderate levels of protein along with essential vitamins and minerals. When finally, Summer arrives, koi carp become significantly more active and their appetites increase substantially. During this period, a good quality growth food should be used. These products contain high levels of protein along with all the vitamins and other trace elements needed for your koi to thrive.

How to acclimatise koi to a new environment

It is crucial to acclimatise a koi to the water if you are returning or introducing it to your pond. You may have purchased a new fish, removed a fish temporarily for treatment, taken a fish to a show or built a new pond. In all cases, your koi should be acclimatised to the water.

The Importance of Temperature

Sudden temperature changes will impact your koi's metabolism and could even kill the fish. Equalising the water temperature between the bag water and the pond is the most important aspect of acclimatisation. Koi can withstand a temperature difference of no more than 20°F. It may be necessary to adjust the temperature of your pond water to ensure that it isn't at too greater variance from the bag water. Koi cope with adjusting to warmer temperatures easier than adjusting to colder ones.

Acclimatisation Steps

The pond into which you wish to introduce your koi should benefit from excellent water quality. The first thing you must do is ensure that your water is pristine. If it isn't, you might have to delay introducing a fish until you have resolved any issues. Float the bag containing the fish in your pond for roughly 30 minutes. Float it for longer if the difference in temperature is greater than 10°F. Then, scoop the koi out of the bag and into the pond with your hands. Discard the bag water and don't empty into the pond as it will contain fish waste and the water will have an unstable pH level. Cover the pond or tank with a net as koi can become jumpy when they find themselves in a new environment. The next step is to place pieces of polystyrene over the net to provide hiding places for the fish whilst it is getting used to its new home. Monitor the fish closely over the next few hours in case any issues arise.

The Traditional Method of Acclimatisation

The traditional way to introduce and acclimatise a koi was to float the bag for a while and then to open it up and add pond water to it. This process was repeated until the bag would barely float and then the koi was released. But it is now thought that it is more beneficial to get the koi out of the bag as quickly as possible, prioritising releasing it over equalising all of the water parameters. A change in pH levels is thought to be less dangerous than leaving a fish in bag water which is high in ammonia. Every koi keeper will refine their own technique for acclimatising their fish and will discover what works best for their stock. Outcomes may vary from one specimen to another and so it is important to monitor your fish closely throughout the process. You might find that you have a sensitive soul in your pond that requires special treatment! If in doubt, seek help from an experienced keeper who can visit your home to lend a hand.

Koi Quarantine Tanks

It is always an exciting time when you are about to introduce a new fish to your pond. Whether you are a very experienced keeper, or are just starting out on your adventure, the arrival of a new fish is a significant occasion. But before you get carried away, remember that you should quarantine your new specimen if you don’t want to put the well-being of your entire stock at risk. Therefore a quarantine tank is an essential investment!

Water Temperature

Before placing for koi into the quarantine tank, ensure that the water temperature is similar to that of the bag or container which your fish has arrived in. Otherwise your new specimen may suffer a temperature shock. The quarantine tank then provides a valuable steppingstone for your new koi before they are introduced to your pond.

Health Monitoring

The quarantine tank gives you the opportunity to monitor the health of the fish whilst they acclimatise themselves to their new environment. The tank should hold between 50 and 250 gallons of water and must have its own equipment including handling nets if you are to avoid the potential for cross-contamination. The tank will require a primed filter with a good build-up of bacteria, a heater and a thermostat.

Travel Stress

Your new fish may be feeling stressed and this can lower its resistance to disease. You can make their transition a more relaxing affair by creating the right temperature in the tank. If your fish was transported in a plastic bag, float this on the surface of the water for a few minutes to equalise the temperatures. If it begins gasping for air, then open the bag. If the fish is lethargic, add some of the tank’s water to the bag and let the koi float for 5 minutes.

PH Levels

When the flotation period is complete, check the pH levels of the bag water and the tank water as they should not differ by more than 0.2. If they do, add more tank water to the bag until the levels match. You can then release the koi into the tank. Place netting over the tank to prevent the koi from popping out and leave your fish to acclimatise to its new home.

Ongoing Checks

Over a period of three weeks, keep a close eye on your new fish. Make sure that it is active and eating well. Look out for signs of disease and treat any conditions that you discover. Change 20% of the water every day and keep the water temperature at the ideal level for your koi’s immune system which is 72 degrees.

Stress Free Introduction

The quarantine tank is a safe and stress-free place for your fish to get used to its new circumstances. It gives you the time you need to assess the health of your koi before releasing it into your pond. When it is time for your fish to join the pond you will be able to release it with confidence.

Is soft water better for keeping koi?

There is a theory that soft water promotes koi growth and impressive colour. However, the available science indicates that the fish are more likely to thrive in water with a DH level (degrees of hardness) of no lower than 6. Hardness is most commonly expressed as milligrams of calcium carbonate equivalent per litre. Water containing calcium carbonate at concentrations below 60 mg/l is generally considered to be soft.

Some koi keepers have alleged that soft water is better when keeping koi. They believe that very soft water encourages enhanced growth and improved colour development. But they are wrong! Freshwater fish, including koi, should be kept in stable conditions and in water with a PH between 6 and 9. The degree of hardness should be no lower than DH6. The degree of hardness is made up of two factors – KH and GH. KH is a measure of temporary or carbonate hardness and GH a measure of the total dissolved minerals in the water. GH is hard to change whereas KH can be altered relatively easily, both intentionally and accidently.

What is osmoregulation?

Koi find the process of osmoregulation much more difficult in softer water. Osmoregulation is the process during which the fish pass salts into their bodies and expel water and ammonia back into the pond. In soft water, the difference in salt concentrations results in the Koi having to work much harder to prevent the salts within their bodies from diffusing out through their gill membranes.

Harder water enables the fish to reduce osmoregulation and they will then experience less stress. If the koi become stressed due to struggling with osmoregulation, their immune systems will be weakened, and they will be prone to disease.

The problem with soft water

Soft water inhibits the process of osmoregulation. This is the process by which the fish absorb salts into their bodies and then expel water and ammonia back into the pond. If osmoregulation is inhibited, the fish will become stressed. Increased levels of stress will impact their immune systems and potentially lead to disease. Soft water with a lower KH is much more vulnerable to sudden changes in the pH level and as this controls the pH level of the Koi’s blood, sudden changes are bad news!

Hard water protects fish from toxins

In addition, hard water holds toxins more effectively, preventing them from passing to the koi. This particularly true when it comes to metals. Copper zinc and lead dissolve much more readily in soft water. KH (carbonate hardness) also provides energy for nitrifying bacteria, in other words, the good bacteria that eliminate ammonia and nitrite. So, it won’t come as any surprise that hard water helps the biomass in the filtration system as the bacteria are better able to flourish.

In other words, hard water helps the biomass in the filter to better prosper. You may experience unintentional changes to the KH and GH levels in your pond. KH is a measure of alkalinity while GH is a measure of the total dissolved minerals in the water. It is important to note that ceramic media can strip calcium from the water and this can impact both KH and GH levels. If you utilise ceramic media, it is crucial to test the hardness of your water regularly and to keep a mineral pack to boost hardness when required.

There is no scientific evidence that soft water helps koi to grow faster or than it enhances colouration. However, it is accepted that soft water prevents red colouration from breaking down or developing the black areas known as shimmies.

What’s the science?

There is no scientific evidence that soft water promotes koi growth or that it enhances their colouration. However, it is accepted that red colouration is supported by soft water and is less likely to break down.

Adding salt to your water

Bicarbonate ions buffer the water, reducing any PH changes, another cause of stress in Koi. Koi fare best in a carbonate hardness of 150-300 mg/litre or 9-18 degrees of hardness. In most Koi ponds the water is too soft due to the fact that there is no natural mud bottom that leaches minerals into the water. Marine salt and sodium bicarbonate increase hardness and so will also cause the pH to rise.

A permanent salt solution of 0.1% is best for Koi. Check your pH level if you add salt, and do not use table salt. The salt used to make saltwater aquariums is the best choice. Salt will not evaporate out of the water and needs to be replaced only if the pond water is drained for any reason.

Changes in pH levels

Soft water facilitates dramatic swings in pH levels. Fish require a stable pH level between 6 and 9. However, acid rain storms or water changes can cause significant and immediate changes in softer water which will affect the pH level of the koi’s blood.

Don’t use tap water

You should never fill or replenish your koi pond with water straight from the tap. Tap water contains numerous toxins including chlorine, ammonia, aluminium sulphate, sodium hydroxide and chloramine. These are toxic to koi in very low concentrations. The amount of toxins in tap water varies from one area to another and can fluctuate dramatically within the same area. For instance, your local water company may choose to add extra chlorine to the water in order to neutralise pollution when they are conducting infrastructure repairs.

In short, you don’t know what is in your tap water from one day to the next and so water must be purified before finding its way into our pond. The majority of issue with koi are caused by the quality of the water. Make sure yours isn’t too soft!

How quickly should you turnover the water in your koi pond?

You may have read that it is advisable to turnover the entire volume of water in your pond every hour which might not be feasible in a larger pond. It is vital to turnover the water in your pond at a sufficient rate to remove ammonia and nitrite from the water. But what is that rate?

Think before you increase waterflow

If you are fortunate enough to own a large koi pond, turning over the water every hour would require an impressive filter system and truly scary energy consumption! Before you plan to construct your own power station, it is important to consider that issues with nitrite and ammonia are less common in larger ponds.

The smaller the pond, the more likely it is to be overstocked and the harder it is to keep the water quality stable. Larger ponds can sustain slower turnover rates and you will probably find that a turnover rate of 2-4 hours is ideal unless your pond is enormous. You can test your water regularly using a proprietary kit but if you do discover ammonia in the water, merely speeding up the turnover rate may not help and might actually prove to be counterproductive.

Is your pond filter too small?

Poor water quality would most likely be the result of a using a filter of insufficient size. Speeding up the water flow will merely result in the pond water passing too quickly through the filter for it to process it properly.

Bear in mind that your pond’s surface, walls and floor will be colonised by the same bacteria that feature in your filter. The larger the pond, the larger the surface area, giving you a bigger bio-filter. Turning up the flow may achieve nothing more than a huge electricity bill!

In larger ponds, poor water quality will usually be the result of inadequate filtration or overstocking. Attend to these potential issues before considering adjusting the turnover rate of the pond.

It is possible to achieve outstanding water quality in a 30,000 gallon pond, for instance, with a turnover rate of 16 hours, providing the filter is up to the task.

Why does inadequate filtration time promote algae growth?

It is the breakdown of dissolved organic carbon compounds into simple inorganic compounds which is the most time-consuming aspect of filtration. The resulting compounds are ultimately incorporated back into living organisms.

This complex process is never instantaneous and will, even under ideal circumstances, take some time. It isn’t hard to see that if insufficient filtration time is available, intermediate products will be pumped out of the filter back into the pond. Which rather defeats the object of having a filtration system! Inadequate filtration often leads to excessive algal growth occurring because the filter is merely producing a generous supply of plant nutrients!

You have a delicate balance to strike if you are to achieve optimum water quality in your koi pond. It is possible to indulge in complicated calculations but ultimately, trial and error might be the only way to find the perfect combination of filtration, turnover and stock levels.

How Fast Do Koi Grow?

Under the right conditions, the average Koi will be between 6 and 8 inches by the end of its first year, and by the time it is 3 years old it will have reached its full adult size.

Koi Growth

An average Koi is able to grow to between 24 and 36 inches in length, although some ‘jumbo’ varieties of Koi are capable of reaching up to 52 inches. Impressive sizes are only achievable, though, if the pond conditions are optimal and if the pond itself is large enough. In any case, getting your Koi to grow to these formidable sizes is not going to be an easy task.

When it comes to the size of the fish, especially if you are attempting to breed the larger varieties of Koi carp, there are several factors that need to be taken into consideration. These include:

  • Genetics
  • Age
  • Water quality
  • Pond temperature & size
  • Nutritional blocks

Koi Genetics

Genetics of the Koi play a huge role in determining just how large the fish is going to be, and if a particular Koi does not possess the required predetermined traits, then it simply will not grow into a large specimen - regardless of how ideal the pond environment may be.

Due to genetic predispositions, most Koi will reach a size of 20 inches if cared for properly and in the right environment.

Under the right conditions, the average Koi will be between 6 and 8 inches by the end of its first year, and by the time it is 3 years old it will have reached its full adult size.

Breeding Large Koi Carp

If you are hoping to grow larger Koi, then you should start with a young female. Try to select one with a large head and backbone. Of course, if you can find out about the lineage of the fish (did it come from large parents) then that will also give you a head start. Diet is a major influence in the growth potential of Koi carp, and it should be looked into carefully. Two of the most important things to remember are the fact that fish are grazers and if fed too much, a lot of it is simply wasted. High protein feed, such as Saki-Hikari, should be given in relatively small amounts 5 or 6 times a day. Another thing to keep in mind is the hormones which are released into the water by the Koi carp. When these hormones reach a high enough concentration, the Koi will simply stop growing (egg production will also stop). This how they maintain a natural balance in the wild and prevent over population. Two things to keep in mind here, then:

  • Low numbers of fish in your pond
  • Good water quality

These two steps alone will go a long way in helping to promote growth in your Koi carp. 250 gallons per Koi is ideal regarding water volume. Keeping to this ratio and maintaining good water quality will enhance your chances of achieving impressive growth.

Most keepers use outdoor ponds for their Koi and this is preferable to indoor aquariums for multiple reasons including the natural day/night cycles and also because of the feeding opportunities that insects present.

How Long Do Koi Live?

Most pond keepers can expect their fish to survive for between 20 and thirty years.

The oldest known carp was a wonderful specimen called Hanako in Japan who lived to the incredible age of 226! Hanako died in 1977 and it was possible to accurately assess her age by analysing the rings on her scales. She was a beautiful scarlet koi which measured 70-cm in length. She was older than the United States! So koi can live up to 226 years but Hanako was a remarkable fish. Whilst many koi have lived to 70 years and more, Hanako's extreme longevity is far from typical.

Koi Care and the Pond Environment

In common with all creatures, a koi's lifespan will depend on the quality of their care and the nature of their environment. It is important to invest in good quality specimens for your pond and then to provide the correct diet and to ensure that the pond environment is a healthy one. Most pond keepers can expect their fish to survive for between 20 and thirty years.

Think Carefully!

The longevity of koi is certainly a consideration if you are thinking about keeping these fish. They could be with you for three decades and, with the right pond, they could live even longer. Koi represent a significant commitment and so you should think carefully before establishing a collection.

Superior Ponds

In superior ponds with the finest filtration systems and a large volume of water relative to the level of stock, the fish can live for forty years and more. Lifespans vary and will be dependent on genetics as well as the quality of the pond environment.

Koi Breeding

As with any pedigree pets such as cats and dogs, the different varieties of koi will enjoy varied lifespans. Koi that have not been subjected to selective breeding tend to live longer than special varieties such as the Gosanke koi which may only survive for 25 years even with optimum care and the finest pond environment.

Koi in Japan

However well you care for your fish, you cannot rival the environment offered by the long-established lakes and naturally fed mud ponds found in Japan. These are the historic home of koi and in these environments, the fish often live for 70 years and more. These fish are never subjected to cement and lined ponds and thrive in the purity of the mineral-rich spring water.

The Beginners Guide to Koi Varieties

Koi, or Nishikigoi as they are more properly known, exhibit a dazzling array of different colours, patterns and scalations. The possibilities are endless, but breeders have established certain desirable traits and identifiable combinations of traits in order to classify a number of varieties. If you have become baffled by the world of koi, then here are the principle varieties to look out for:


Kōhaku are koi with white skin featuring large red markings. The best Kōhaku have blemish free white skin with deep red, evenly distributed patterns. Kōhaku appropriately means red and white. This was the first ornamental variety to be established in Japan.

Taishō Sasnhoku (or Taishō Sanke)

Taishō Sasnhoku (or Taishō Sanke) are similar to Kōhaku but also boast small black markings which are called sumi. Prized fish possess the same qualities as Kōhaku but with the addition of the black markings. There are several variations of the Sanke including Doitsu Sanke, Maruten Sanke, Tancho Sanke and Din Rin Sanke.

Shōwa Sanshoku (or Shōwa Sanke)

Shōwa Sanshoku (or Shōwa Sanke) are koi with a black base and red and white markings. These fish are commonly known simply as Showa and can be confused with Taisho Sanke. However, with Showa the black markings wrap all around the body instead of appearing only on the top and there will always be black on the head. The most valued Showa have colours balanced evenly about the body with clearly defined edges to each colour. Variations include Tancho Shōwa, Maruten Shōwa, Gin Rin Shōwa, Doitsu Shōwa and Kin Shōwa.


Tanchō describes any koi with a single red patch on its head. Sub varieties include Tanchō Shōwa, Tanchō Sanke, or Tanchō Goshiki but the term is usually used to describe Tanchō Kōhaku. This variety is named after the Japanese crane which has a red spot on its head. The quality of this variety is determined by the symmetry and location of the red marking.


Chagoi means tea-coloured but these koi can vary from pale olive green or brown to copper and deep shades of orange. They feature solid colour and a subtle but noticeable reticulated net pattern. They are valued for their friendly nature which makes them amenable to hand feeding and they tend to be large in size.


Asagi are koi which have a blue net pattern on their backs and red or orange on their undersides, gill plates, fins and body. The most prized specimens have a red pattern which does not extend above the lateral line.


Utsurimono are black koi with either white (Shiro Utsuri), red (Hi Utsuri) or yellow (Ki Utsuri) markings. The resulting bi-colour pattern is often similar to a piebald horse or a bold snakeskin. This variety began with breeding of black and yellow koi.


Bekko are white, red or yellow koi with black markings called sumi. The Japanese name means tortoise shell. These fish are easily confused with Utsuri.


Goshiki means five colours. These koi have a solid white base with a black and blue edging and then red and black patterns overlaying the base.


Shūsui means autumn green and these koi are the scaleless (doitsu) version of Asagi. Here the blue net pattern is replaced by a single row of scales along the dorsal line. As with Asagi, the belly, gill plates, sides and fins of Shusui display an orange or red pattern.


Kinginrin are koi with metallic scales. The name is often abbreviated to simply Ginrin. There are Ginrin versions of almost all other varieties of koi, and they are highly sought after. Their sparkling, scales are in contrast to the smooth, metallic skin of the Ogon varieties. Recently, these characteristics have been combined to create the new Ginrin Ogon varieties. (How confusing!)


Kawarimono is a generic term for any koi that cannot be identified as one of the recognised varieties. Such specimens can also be known as Kawarigoi. ōgon are koi with a metallic appearance and are of a single colour. The most commonly seen colours are gold, platinum, and orange. Cream specimens are very rare. The best examples benefit from unblemished skin with absolutely no marks or patterns.


Kumonryū are black and white scaleless (Doitsu) fish with curly patterns. The patterns are thought to be reminiscent of Japanese paintings of dragons. These koi are fascinating because they change their patterns many times during their lives. The sub variety Beni Kumonryū feature a third colour.


Ochiba are a light blue/grey koi with copper, bronze, or yellow patterns. They are reminiscent of autumn leaves on water. The Japanese name actually means fallen leaves.


Goromo are white koi with a Kōhaku-style pattern featuring blue or black-edged scales but only over the red pattern. This variety first appeared in the 1950s and is a cross between a Kōhaku and an Asagi.


Hikari-Moyomono are koi with coloured markings over a metallic base. In Japanese Hikari Moyo literally means 'metallic pattern'.

Kikokuryū / Beni Kikokuryū

Kikokuryū means sparkle and denotes a metallic-skinned version of Kumonryū, with standard colours of black and white.

The Beni Kikokuryū is just like a Kikokuryū, it is also scaleless (Doitsu) and metallic. The primary difference is that Beni Kikokuryū have a red or orange pattern overlayed.

There is a lot to take in isn't there? Perhaps you can now start to recognise the many different varieties of koi. If you are interested in keeping koi, then it could be a good time to decide which varieties you favour and would like to keep or breed. With the fabulous range of koi food here at Krafty Koi you are sure to nurture the finest specimens.

A Guide to Feeding Koi

A good diet will ensure that your Koi thrive, and it is important to neither over or under feed your stock. Choose a good quality Koi food and remember that your feeding regime will be largely dictated by the temperature of the water. Koi's metabolisms slow down considerably in low temperatures and so they require less food in the winter months and sometimes will not need feeding at all.

Temperature Ranges

Water Over 30° C

Koi can lose their appetite when the water reaches a temperature in excess of 30° C. Feed Koi no more than twice each day when the water temperature is this high. Provide easily digestible Koi food such as wheatgerm and try to reduce the water temperature by shading the pond. Baby Koi's eating habits are less affected by high temperatures.

Water 20° C to 30° C

Koi are at their most active in this temperature range and so you can feed them two to four times each day with their usual feed or with feeds formulated for colour enhancement and growth. You can feed more often if you provide smaller amounts at each serving.

Water 15° C to 19° C

Your Koi's digestive systems will start to slow down at these temperatures. You should monitor their activity levels and reduce the volume of food that you provide accordingly. It is best to feed at the warmest time of the day. You will need to feed your stock only once or twice each day.

Water 10° C to 14°C

It could be time to switch to easily digestible winter feeds which are principally made up of wheatgerm. Feed no more than twice each day and don't feed your fish unless they seem keen to eat. You can test their appetites by sprinkling just a little food onto to the water.

Water 5° C to 9° C

Feed only two to three times weakly and only provide winter food. Feed if your Koi are active and in quantities that are consumed in one minute.

Water Below 5° C

Your fish should now be hibernating and will not require feeding.

General Guidance

Always strictly control the amount of food that you offer. Only feed an amount which is consumed within two minutes. If you have leftover food after this time you are overfeeding. Any leftover food should be removed immediately so that it does not rot and then pollute the pond. If there are any sudden changes in the pond environment such as a drop-in temperature or fish start becoming ill you should stop feeding or at least reduce the volume of feed until any issues have been resolved. If you have stopped feeding in the winter then when the water begins to warm up in the spring, reintroduce food gradually. Start with winter foods and then introduce your Koi's staple diet. Always err on the side of under rather than over feeding if you wish to maintain a healthy environment in the pond. Try to stick to Koi food rather than human food as this is formulated to provide the correct nutrition for your stock.

Feeding koi by hand

Interacting with the koi in your pond on a more personal level is not only a source of great fun, but it can also be a very rewarding experience. Koi (like humans!) are known to have changes in mood and this is all related to how comfortable and safe they feel in their environment. One way to ensure that they remain happy is by building a relationship with them through this act of hand feeding. By the stage that your koi are at ease with you and the home you have given them, you'll have them eating out of the palm of your hands!

One of the first things to attend to even before you attempt to build this relationship is the pond conditions. By observing the movements of your koi, you will be able to see if they are at all anxious, stressed or scared in their environment and that is all to do with the conditions of the pond and its surroundings. Take care of this and you will have happy koi, and with happy koi you might just have yourself some long-lasting friends.

Making your koi comfortable

It might seem odd to call your koi friends, but it is the case that koi have quite impressive memories, loyalties to their owners (and food providers!) and also individual personalities. Evidence to suggest that koi remember a face, much like a dog, indicates that it is a more than worthwhile endeavour to build a relationship with them up close and personal. Not only that but, by getting close to your koi at feeding time, you will be able to inspect them for any signs of injury, disease, or other health related issues which might be present.

So, what is the key to getting your koi to come up to you at feeding time? Well, one of the most important things to consider is location and timing. As koi have an evolutionary suspicion of anything approaching the pond at random times in the day (as they construe such an occurrence as the sign of a potential predator) it is crucial to come to the pond at the exact same time in the day each day, and also approach the water from the exact same spot. With your koi attuned to this consistent routine, they will understand not to be wary or afraid.

Building a relationship

Also very important is to temporarily cut off feeding and then after six days or so recommence by throwing small amounts of food in one spot nearest to you in the pond whilst either standing or sitting close by to the water's edge. As the koi are hungry, they may well venture over. But, if they do not then have no fear! Though they might not yet have been comfortable enough to approach, they will have seen you and so the next few times you approach (at the same point in the day and at the same spot by the pond) they will be more likely to come over.

Eating out of the palm of your hands!

Soon enough, after consistent repetition, they will be associating you with feeding time and will come over to feed at that spot. At this stage, try to pinch the food in your hand above the water and they should start to be confident and comfortable enough to take the food from your hand. And from there, the relationship will grow stronger and stronger. The only things you need to bear in mind is that you should wash your hands thoroughly before and after feeding time, and also that, whichever way you are feeding you koi, the quality of the food remains paramount.

Enhancing Colour in Your Koi

Koi Carp exhibit a range of brilliant colours. It's the spectacular colouration which distinguishes Koi and that endears so many people to keep these particular fish. Whether you're interested in competing for a prize-winner or simply want your specimens to look at their best, it is important that you promote excellent colour in your fish. To do this you must ensure that they enjoy the right environment and are fuelled with the correct diet. An unhealthy or stressed Koi will quickly show signs and their beauty will fade.

The Healthy Pond

Poor water quality is the primary cause of most health issues in Koi. The fish will quickly become stressed and the strength of their colours will be affected. Clear water does not necessarily mean good quality water and so you should test your pond regularly to ensure that you are providing the best environment for your fish so that they may thrive. Koi colouration can also fade if the water becomes too hot, so monitor your water temperature closely during the summer months. Definitely provide shade if your pond is likely to reach 85 degrees or more. At this temperature your fish's digestive system is far less efficient. Water quality can be impacted because oxygenation is reduced, and beneficial bacteria become less efficient at processing waste. Take care not to shade your pond for too long as Koi require a measure of sunlight to exhibit the finest colours. Whilst the strength of colour that your Koi display is partly down to genetics, even the finest specimens will begin to fade in poor conditions.

Koi Food

It is imperative that your fish receive a nutritious diet both for colour enhancement and general good health. To ensure this you should select high quality foods to provide a balanced diet and during the primary growth period, give foods which include colour enhancers. This will be when the water temperature is at least 70 degrees (generally June to early September). You must capitalise on the opportunity to enhance the colour of your fish at this time of year. Revert to a lower protein diet free of colour enhancers at other times.

Colour Enhancers in Koi Food

Many Koi foods contain natural colour enhancers. It is carotenoids which work their magic on colour, and these are found in many Koi food ingredients including shrimp, krill, paprika, marigold flower and spirulina. Spirulina is a tropical plant algae that is extremely high in protein. Indeed, it boasts the highest protein content of any natural food. You should take care not to over feed colour enhancers as they can lead to discolouration of white areas of your Koi. These could take on a yellow, brown or green tinge. In this scenario the discolouration is caused by the effect that carotenoids have on light rather than because your fish's pigmentation has actually changed. White skin cannot feature red pigmentation as it does not have the necessary red chromatophores.

Artificial Colour Enhancers

It is also possible to feed your Koi artificial colour enhancers. Astaxanthin and Canthaxanthin are powerful sources of colour and must be provided in carefully measured doses. You should seek expert advice before using either of these.

Do Koi Eat Goldfish?

Koi could eat small goldfish but it's not all bad news as they most likely won't, also there's plenty of other species that will also happily share a pond.

Which Species Can Share a Pond with Koi?

Koi carp thrive in ponds that have a large capacity, a generous amount of cover and efficient filtration. They need excellent water quality and a deep pond. But they are resilient to cold temperatures and can withstand harsh winters providing you feature an airstone or floating heater to ensure that there is an exchange of gasses. Given the size of koi and the nature of the habitat that they require, there are several fish with which they can live quite happily.

Golden Orfe

Golden Orfe (Leuciscus idus) do well in ponds with good filtration and are bottom feeders. They are sociable fish and so you should include at least three specimens in your pond.


Goldfish are also worth considering and can live in the same pond as koi, but they may interbreed, and this can result in rather ugly hybrids! Koi could eat small goldfish so be wary of featuring small specimens in your pond as they may start disappearing! The best species of goldfish to share your pond with your koi are comet goldfish. Goldfish breed well and so you should ensure that you don’t end up with an overstocked pond.


Tench are peaceful bottom feeding fish which are also compatible with your koi pond. As they tend to dig a little when feeding, they disturb any silt or debris at the bottom of the pond enabling the filter to remove it more efficiently.


You could also consider including barbel. These fish keep close to the bottom of the pond and keep it clean of food which has been missed by the koi. They need good water flow otherwise barbel have a tendency to develop deformed spines.


Sturgeon could be a good choice. These fish disturb debris at the bottom of the pond and so give the pump a better chance of driving it to the filter. Surgeon enjoy the depth and lack of vegetation. But some species can grow very large, so it is vital that you have a pond of an appropriate size. Your pond will need to have a volume of at least 1000 litres but should preferably be three times this size to host sturgeon.

Potentially Problematic Species


Pleco can coexist with koi and are effective at removing algae but do not tolerate water temperatures below 55° F and so would have to be removed from the pond for the winter. Catfish can live with koi for a while, but larger specimens could attack and kill the koi. These fish may also promote disease.

A Guide to Disease in Koi

Koi carp can fall prey to a variety of diseases. Your Koi rely on you to provide a healthy environment in their pond and to ensure that their lives are stress free. Diseases in koi usually result from the following issues:

  • High ammonia levels in the water
  • Low oxygen levels
  • Handling the fish
  • Poor water quality
  • Overcrowding in the pond
  • Parasites
  • Incorrect water temperature
  • Toxic chemicals
  • Sharp edges in and around the pond
  • Inadequate or incorrect nutrition

It is essential that you identify the signs of disease at the earliest opportunity and then take the appropriate steps to tackle any conditions that you discover. Here are the diseases that you should look out.


This is one of the most common diseases found in Koi and is also known as White Spot Disease. The first symptoms of Ich are the appearance of small white parasites on your fish. These look like grains of salt. Ich is usually the result of poor water quality and so you will have to address both the disease and its causes. To treat Ich, you should first increase the salt concentration of your pond to roughly 0.5% over a period of a few days. The water temperature should be increased to 80°F and aeration should be improved. Alternatively, you can address Ich using Malachite Green and Formalin. Both treatments are best carried out using a quarantine tank.


This is also known as Pinecone Disease and is generally the result of poor water quality. Koi carp suffering from Dropsy often exhibit swelling or lifting of the scales. Their eyes may also bulge. Again, it is best to quarantine any affected fish although the condition is not highly contagious. Dropsy is almost always fatal once the symptoms are visible as they are indicative of kidney and liver failure.

Tail Rot

Tail rot and fin rot are secondary conditions caused by stress or poor water quality as either can compromise the auto-immune system. This is a bacterial infection which is best treated by changing the water in your pond and increasing the levels of salt. Necrotic tissue may need to be trimmed under sedation and severe cases can be treated with antibiotics.

Mouth Rot

This condition causes sores in the mouth and is often caused by poor water quality. You should address the cause by improving the environment in the pond. The sores can be treated with hydrogen peroxide or iodine.


This condition is a killer and is caused by a leaf shaped protozoan parasite. Fish may roll over on their sides and exhibit laboured breathing and lethargy. They may also try to rub against an object in the pond. Treatments include formaldehyde used as a bath, Methylene Blue as well as the drug Acriflavine.

Aeromonas and Pseudomonas Bacterial Infections

These bacteria can cause ulcers and fin erosion. The infected fish will require Chloramphenicol injections for Aeromonas infections and Baytril injections for Pseudomonas infections.


The Columnaris bacteria will attack wounds causing fin, tail and mouth rot. Fish can also develop a white film on their skin and exhibit sunken in eyes. This infection is also known as Cotton Wool Disease and can quickly prove fatal. It can be treated via a bath in Mebromin, Potassium Permanganate, or Methylene Blue.

Anchor worm

Anchor worm is also known as Lernea and is a crustacean parasite that attaches to koi and feeds causing damage to the tissues of the fish. The worms can be removed using tweezers. Neosporin should then be applied to the infected area. Dimilin, Dylox or Lufenuron can be used to clear the pond of Anchor worm.


Argulus or fish lice are parasites which cause irritation, and which can lead to bacterial infections. The irritation will cause the Koi to rub themselves against objects to gain relief. Treatment is as per Anchor worm.

Fungal Infections

This type of infection is not contagious and usually begins with a break to the skin. Fluffy growths will appear which may have a green tinge. Raised bumps can form on the fins. The fungus should be removed by rubbing the area with a swab and then an antibiotic cream should be applied.


This is a virus which is not highly contagious. It causes discolouration of the skin and sometimes lesions. This condition often occurs following a change of water temperature. The afflicted fish should be quarantined in a tank in which the water temperature is raised. However, sometimes this virus clears up on its own. It can also be treated with products containing neutral Acriflavine.


Epistylis is a rare parasitic infection that can cause other diseases in your Koi. It is usually the result of poor water quality. The parasites look like a fungus and promote the formation of white tufts around wounds and ulcers. You should quarantine the affected fish, change the water in the pond and increase the concentration of salt in the water.

Skinny Disease

This disease is caused by a bacterial infection. The affected Koi exhibit a sucked-in gill appearance and an enlarged head. This condition can be addressed by providing additional food or by adding erythromycin to the feed.

Carp Pox

Carp Pox is a common condition and not particularly contagious. It is rarely fatal but may disfigure the fish. It causes waxy raised growths which are pinkish in colour. There is no treatment for Carp Pox and it usually clears up on its own but heating the water may help to speed recovery.


This disease is also known as Hole in the Head disease and is caused by a protozoan parasite. Koi may become lethargic and skin lesions can develop. An affected fish will often seek isolation in the pond. The afflicted fish should be quarantined and treated with Metronidazole or medicated food.


Flukes are incredibly small and so you will need a microscope to verify their presence. Dactylogyrus or gill flukes attach to the gills whilst gyrodactylus flukes attach to the body. They are parasites which feed on, and therefore erode, the slimy coating on the skin of the Koi. This exposes the fish to infections and causes irritation. If you have specimens afflicted by flukes, then the entire pond could be affected and must be treated with a proprietary product containing Praziquantel. You should routinely treat your water in the spring and autumn.

Velvet Disease

This is a condition caused by Oodinium parasites. Your koi will acquire a velvety golden dusting and may lose scales. This is a rare condition which can be treated by adding Formalin to the water.


Like flukes, Costia are tiny parasites which reproduce rapidly. Koi generally do not suffer from Costia unless they are already debilitated. If fish are affected, then this usually happens in spring. Koi will seem lethargic and will try to rub against the sides of the pond. The affected areas take on a white/grey hue and the Koi's fins may redden. If the parasites afflict the gills the fish may be seen gasping at the surface of the water. Costia can be treated by adding Malachite Green and Formalin to the pond but you must ensure that there is no salt in the water prior to treatment. You could also consider adding Acriflavine. The affected fish can be given a salt bath to aid recovery.

Pop Eye

This condition is also known as exophthalmia. It is a response to excessive fluid or gasses behind the eyes and causes the eyes to bulge. The affected fish should be given a salt bath.


Leeches feed on the koi's blood and will eventually kill the fish if left untreated. They can also transmit the disease SVC. The leeches will be visible on the body. Proprietary treatments in powder form are available.

Saprolegnia Fungus

This is a common fungal infection found in Koi. Spores from this fungus can grow on any part of the fish. The fungus attacks the Koi by germinating on any dead tissue. The juices released to break down this tissue will eventually start to kill living tissue. The fungus looks a little bit like cotton wool and usually only attacks fish with damaged skin. The condition can be addressed by quarantining the fish in water which is at least 77°F and by raising the salt level to 0.3%.


This is a protozoan parasite which causes Koi to display a grey/white opaque appearance. The parasite damages the Koi's tissues and can afflict the skin and the gills. The fish may appear lethargic and will rub themselves on the side of the pond. Trichodina can be treated by raising salinity to 0.6%. A course of Formalin may also be required.

Koi Herpes Virus (KHV)

As the name suggests, this disease was first discovered in Koi, the ornamental varieties of carp, but over time it has come to affect common carp populations too. Every summer there are numerous outbreaks of Koi herpesvirus in UK fishing lakes. The outbreaks occur in warmer temperatures and then fisheries find themselves having to implement controls to restrict the spread of the pathogen. Outbreaks are most common between mid-June and September. This is a potent virus which results in sloughing off of the skin. This sloughing can then leave the fish open to infections. Your fish will be lethargic and will develop lesions on its skin, gills and fins. KHV must be treated in haste by increasing salinity to 0.45% and raising the water temperature to 87°F. Medicated food may also be required.

The Koi herpesvirus (KHV) was first recorded in the USA and originated in ornamental Koi that had been imported from Israel. The disease arrived in the UK in 2002 and for a time was restricted to Koi in garden ponds. It then found its way into the wild common carp population. The spread may have been caused by pet fish being released into the wild.

KHV is highly contagious but poses no threat to humans or mammals. It only infects carp. The disease mainly affects the fish’s gills. Lesions form which become infected with bacteria and fungi. Further symptoms include sunken eyes, blisters and pale patches on the skin. The fish may also display erratic behaviour including disorientation and hyperactivity. Infected specimens may detach themselves from the shoal. Most of the infected specimens will unfortunately die but the mortality rate will depend on the water temperature and the density of the fish population. Fish can die within 24 hours of the onset of symptoms. It is thought that any infected fish which survive the disease remain carriers for life. Outbreaks occur principally when water temperatures reach 15 degrees or above. This usually means that the first reports of outbreaks in the UK occur in June. Under UK and EU legislation, KHV is classified as a notifiable disease. This means that it is subject to national control measures because of its potential environmental impact and the fact that it is untreatable. There is no vaccination against infection.

Gill Maggot

This parasite often attacks the Koi's gills and has a maggot-like appearance. It causes irritation to the fish. Seek out products effective against maggots and increase aeration to address the issue.

Bent Koi

You may notice that your koi are taking on a rather bent appearance. This could be the result of scoliosis which is caused by a deficiency of ascorbic acid in the diet. Scoliosis can be treated by feeding foods high in Vitamin C. The condition can also be due to electrical discharge in the water. This would be caused by damaged submerged pumps. Bent Koi might also be the result of an air bladder infection. This will probably require antibacterial injections. As you can see, they are many conditions which could afflict your fish. It can be difficult to identify specific conditions as there are symptoms common to several diseases. If in doubt, seek expert advice. We have only provided a brief explanation of each condition and this may be insufficient to enable you to make an accurate diagnosis.

8 ways you could inadvertently kill your koi

Koi keeping is an increasingly popular hobby. The fish are fascinating and provide a colourful addition to any garden. But while koi are hardy fish which are well-adapted to living in a variety of climates, they do have specific needs. If you are new to keeping koi, it is easy to make mistakes and to fall short of meeting the basic needs of the fish. Here’s eight ways that you could kill your koi.

  1. Pesticides: We know that you wouldn’t deliberately pollute your pond with pesticides. However, in heavy rain, runoff can find its way into your pond water and bring pesticides from the environment with it. It is important to allow for this fact when planning the construction of your pond and you may need to create a means of diverting runoff away from it.
  1. Infections: Koi can fall prey to viral or bacterial infections. They can generally fight these off but it is important to maintain good water quality and to provide your fish with the correct diet. Keep an eye out for signs that your fish are unwell and act quickly if you have concerns.
  1. Jumping: Koi are natural athletes and may even appear to be suicidal at times! They can and do jump and if they miss the water on the way down, they could perish before you discover that there is a problem. If one of your fish is a persistent jumper, installing a bird net might be a good idea.
  1. Lack of oxygen: Keep an eye on the growth of your fish because competition for supplies is the most common reason for oxygen deprivation. You should stock your pond with the correct number of fish for its size and consider featuring plants to boost oxygen levels. As the fish grow, their oxygen consumption increases. A nicely balanced pond environment can soon become a dangerous one for your stock.
  1. Predators: Your fish represent an inviting meal for predators, and they will be persistent in their attempts to get it. You will probably need a bird net and fencing around the pond. If you don’t protect your fish, you will soon find them disappearing. Once a predator has found out how to access your pond they will keep coming back.
  1. Ulcers: Koi rest on the bottom of the pond in winter and so their undersides are in contact with any substrate. Their bodies could become ulcerated as a result and so it is best if the bottom of the pond is smooth.
  1. Parasites: Koi can be afflicted by parasitic infections. Unfortunately, by the time the koi exhibit visible symptoms, an infection may already be severe. Most infections are easily treatable so the key to success is to carefully monitor the fish for signs that they are failing to thrive. Look out for listless fish, koi which have lost their vibrancy and individuals which will not eat.
  1. Poor Water Quality: The number one cause of koi death in ponds is poor water quality. Always ensure that your filtration system is working well, regularly test your water and don’t overstock the pond.

All About Ozone

Ozone is a naturally occurring, water-soluble gas and oxidiser. It can control many common bacteria and deactivate viruses. So, should Ozone feature in your Koi pond set-up?

How Ozone Works

When Ozone comes into contact with waterborne pathogens one of the three Oxygen atoms detaches itself from the Ozone molecule and then attaches itself to the pathogen. It oxidises it and so destroys it. Ozone is so powerful that the tiniest amounts will offer an effective germicidal action whilst leaving no toxic by-products or residues in the water.

What is Oxidation?

Oxidation is the process that causes metals to rust or fruit to turn brown. The process damages cell structure and so kills simple organisms quickly. Oxidation is how beneficial bacteria remove ammonia and nitrite from ponds by converting the ammonia to nitrite and then to nitrate.

Will Ozone Affect a Bio-Filter?

Ozone will kill harmful bacteria when they pass through an Ozone stream in a protein skimmer. However, beneficial bacteria do not pass through the stream as they live on the filter media. Some will be free-swimming and so will be killed by the Ozone, but this process is balanced by the fact that the good bacteria grow more rapidly in an ozonised system as the entire pond system is cleaner and better aerated.


Ozone will kill algae even if they don't pass through the Ozone stream, as the ozonised environment leaves algae more susceptible to oxidation.

Will Ozone Harm Koi Stocks?

Ozone helps to eradicate simple organisms but is not harmful to more complex organisms such as Koi carp. The Koi never come into direct contact with the ozone stream and any residual gasses are not transferred to the pond water, they are expelled into the atmosphere. It has been argued that Ozone creates a sterile pond environment but there has been no scientific evidence found to support the suggestion that Koi’s immune systems can be damaged by pond disinfection via oxidation. Ozone helps to create a more natural environment in a Koi pond similar to that in a river where the level of bacteria is generally much lower. Marine aquarium enthusiasts have been using Ozone systems for many years and see only improvements in their stock's health. Ozone represents no danger to human health if handled correctly.

Creating an Ozone System

An Ozone system does not replace your conventional filtration system; it should be used in partnership with it and will ensure that it is more efficient. You can still use chemicals in your Koi pond to address parasites, but you must switch off the Ozone generator when you do this as it will destroy the chemicals. Perhaps it is time to consider using Ozone in your Koi pond if you haven't done so already. If your system is correctly installed it could provide the pond environment, you need for your Koi to really prosper.

Protect Koi from Heron - Koi Predators

In the United Kingdom there are a number of species that pose a direct threat to Koi stock. As a Koi keeper, knowing about these predators and how you might protect Koi against them can literally be the difference between life and death for your stock. Exactly what species pose a danger will depend on a number of factors, including what precautions you may already have in place, in which area of the country you live and your proximity to important features in the local landscape, such as rivers and lakes.One predator that doesn't seem to have a restriction on its whereabouts is the Grey Heron.


Without a doubt, the most potent threat to Koi in the UK is the Heron and it also happens to be one of the hardest predators to protect against, but there are some tried and tested ways that you can attempt do so. Heron do not specifically target Koi of course, but when there is a Heron about then all pond-fish are in danger and so the information here is relevant for all pond-keepers with any kind of ornamental fish stock. Like all species Herons are here because quite frankly, they're incredibly good at what they do. The Heron is adept at hunting aquatic prey and they are a common sight in the British Countryside, where you'll see them all year round standing in shallow water waiting out their prey. It's unsurprising that a garden pond and a stock of ornamental fish is a great feeding opportunity for a Heron. Whilst you might think that hunting in a garden or a busy city would increase the chance of the Heron's hunt being disturbed, the captivity of the fish makes the hunt a much quicker process and it's thought that because of its ease, young Herons are often the ones hunting in ponds because of the almost guaranteed catch. In the UK the only type of Heron you'll see is the , although you'll find other members of the Heron family in Egrets and Bitterns.

Measures that you can take to protect your Koi against Grey Heron include:

Use deep water to your advantage

Do not have shallow areas or steps around the edge of your Koi pond. Heron thrive in shallow water, it's their perfect platform for hunting.

Use plant life as cover:

Floating plants and lilies, for example, can give Koi an excellent place to hide from a Heron's gaze. This tactic is not only good for the ecosystem of the pond, but also beneficial should your pond be visited by a Heron. This will also provide some cover should a Heron be flying overhead. Bear in mind the impact of the seasons on plant life and the cover that it will provide.

Pond Netting as a physical barrier

Placed in a way as to cover the pond, Netting can provide a physical barrier between a prying Heron and the Koi stock. In addition to Heron, this method will secure the pond against even the most determined predator. The application of the Pond Net is key and needs to be high enough from the water's surface. Of course, with Pond Netting there is an obvious aesthetic trade off. It's for the pond-keeper to decide whether a Net is the answer or if it's an eye-sore too far that's also a barrier to them enjoying their pond fully.

Decoy Herons

There's mixed reviews over the use of decoys such as fake plastic Herons. There is the thought that placing a decoy close to your pond will deter a real Heron stopping by and some fish-keepers swear by them. It's thought that Herons will not land if another Heron is already fishing in that spot and there may be some logic to this, as how often in the wild do you see Heron hunting in the same immediate area as another? Not very often.


Herons might like koi, but they are wary of people so a scarecrow which looks suitably human might do the trick. This should be backed up by a regular human presence as the birds will eventually cotton on to the fact that the scarecrow isn’t a threat. Even the average bird brain is capable of working that out! Herons are most likely to pay your pond a visit at dawn or dusk, so these are good times to be at your pond if you want to deploy scare tactics. By the way, there is no point investing in a plastic heron to scare off the birds. Heron ornaments of any kind are likely to attract the birds to your pond rather than keep them away. So, there you have it. You can’t kill or injure herons so you must either scare them off or shield your pond. If there is a heron in the area and it has found your garden, you could be in for some serious trouble.

Other fish-keepers that have tried and tested a decoy Heron see little point, as sometimes the real Heron will stop by anyway - ignoring the other plastic bird altogether. A quick image search online will show you plenty of examples of this caught on camera by pond-owners.

Koi Security

Sad stories of lost and stolen Koi are depressingly common. As we know, Koi are often such brightly coloured fish that they're hard to miss and this makes them more prone to falling victim to predators. Koi are also coveted by people; some can have a significant value so it should come as no surprise that they are frequently stolen. A misconception that all Koi are extremely valuable certainly doesn't help.

If your Koi are your pride and joy then you should always be taking steps to protect them because your stock may very well be targeted by thieves of both the four legged and two legged variety. Pond security is not something about which you should be, well... coy!

Secure Your Garden

If it is possible to access your garden from the side of the house then it's wise to fit your gate with a lock and a bolt. The higher the gate and fence the better. Don't allow potential human thieves ready access to ladders or anything else that they can use to scale your gate. Keep any such items locked in the garage or a shed. You should also consider fitting an alarm to your gate or even installing a perimeter alarm if your garden is vulnerable to ingress from the rear. It can help to display a "beware of the dog" sign even you if you don't happen to have a dog!


Both human and nocturnal animal intruders will be far less likely to target your garden if it's illuminated. Outdoor lighting can have other benefits too, such as enhancing the ambience of your garden and pond as well as making your garden safer for you and your family at night. At the very least, where lighting is concerned, fit security lights that are activated by motion sensor.

Secure the Pond

Your Koi carp could potentially be vulnerable to predation by cats, foxes, large birds and more. Netting is, therefore, a sensible precaution. It does always seem like rather a shame to cover a pond with a net but losing your fish as a consequence of not having one is of course far worse. It is also possible to invest in a scarecrow that will squirt water when triggered by a motion sensor. This should see off most animal invaders.

Catching Intruders Red Handed

If you do find that you are losing fish then you need to be able to identify the culprit as soon as possible, otherwise you won't really know what measures you will need to take in order to prevent the same from happening in the future. Other than lying in wait for your invader, your only course of action is to install security cameras. You can then review the CCTV footage, and this should help to reveal the culprits. Security CCTV equipment doesn't come cheap and so perhaps it should be considered as a last resort after other preventative measures have been put in place and overcome.

Electric Fencing

Electric fencing is easy to install and doesn't cost the earth but it's unsightly and is likely to even catch you out from time to time! It could of course also shock your pets. However, an electric fence is an effective deterrent that animals quickly learn to avoid.

Security Round-up

As you'll probably already know, security is a major concern if you keep Koi. Thankfully the vast majority of measures that you can take to foil thieves are relatively inexpensive and most will not have a negative impact on the aesthetics of your pond.

Can you grow plants in your koi pond?

The short answer to that question is only if your fish will let you! Large koi may demolish or eat your plants but adding plant life to your pond is beneficial for Koi. The plants will also lift the look of your pond and transform it into a more beautiful feature of your garden. But you need to choose the right plants and place them correctly so that they are not quickly consumed by the fish.

The benefits of aquatic plants in a koi pond

Aquatic plants are considered to be good additions to any koi pond. They help to increase oxygen production in the water, and they keep the water cooler in hotter temperatures whilst creating shade for the fish. In spring, submerged vegetation provides a surface on which female koi can attach their fertilised eggs. Plants also prevent the spread of algae as the shade they provide limits photosynthesis. Plants create a natural filtration system which restricts the formation of blanket weeds.

How to introduce your plants

The best way to introduce plants into your pond is to build a plant shelf. This can be constructed along the edge of the pond. You should weigh down the plants with large rocks or stones as this will form a barrier between the plants and the fish and so restrict the number which are eaten! Do be aware that the plant shelf might make it easier for predators to feed on the fish and so preventative measures may be required to protect your stock. Floating plants, shallow-water marsh plants and submerged plants can also be placed directly into the pond.

Floating plants

Floating plants feature vegetation which sits on the surface while the roots hang down in the water. With some species, the roots may attach to the bottom of the pond. These plants provide shade for the fish and are generally easy to care for. Consider featuring water hyacinth, water lettuce, water lilies or lotus. Keep an eye on the growth of these species as they can get a little out of control.

Shallow Water Marsh Plant

These aquatic plants are typically planted on the edge of your pond in the shallow water. Consider water iris and horsetail for your pond. Umbrella is also an option but will not survive a harsh winter.

Submerged Plants

These species are grown in pots and then placed at the bottom of the pond. They are great oxygenators and remove excess nutrients from the pond environment but may be uprooted and eaten by the fish. Fanwort, American waterweed and water Purslane are good choices. You might have to experiment to see what really works in your pond. With a little planning, you should be able to plant your pond so as to improve the water quality for the fish while also creating a more attractive look. You never know, you could discover a passion for gardening as well as for koi!

Your Koi Pond in Spring

When spring arrives and temperatures begin to rise, your koi will become more active. It is important that conditions in your pond are perfect for your fish and that you feed your stock correctly as they emerge from their winter fast. Here are our top tips for a heathy pond in spring.

Monitor the water temperature

A floating pond thermometer is a must-have accessory. If you don’t have one, invest in one today! Koi are cold blooded and so cannot regulate their own body temperatures. Their behaviour will be dictated by the water temperature and so it is vital that you know what that is. Your koi should start to become active when the water reaches 50–55F and it is important that you don’t do anything until the water is stable at this temperature.

Koi pond cleaning

If you have rocks at the bottom of your pond, you may need to move your Koi temporarily and clean the pond before you start treating the water and feeding your fish. Debris caught between rocks will impact the water quality and your Koi’s health. Consider removing the rocks as they result in annual disruption for your fish which isn’t beneficial for their wellbeing. The rocks could impact the health of your stock even if you clean your pond every year.

Treat your pond

After a winter of fasting, your fish will be weak and their immune systems vulnerable. It is crucial to attend to any parasitic or bacterial issues before you start feeding your stock. Treat your water with an antibacterial product such as Pond Doctor Anti Bacteria but take care to add the right amount for the volume of your pond.

Activate your filter

Whether you are using a mechanical filter (beads filter) or a biological filter, you may have stopped filtration during the winter. If you did, you need to restart the nitrogen cycle. Clean inside the filter and add beneficial bacteria to the filter or the pond.

Be patient in feeding

Feeding your koi is enjoyable and so you will probably be anxious to get on with it, but don’t rush! Your koi may not be quite ready, even when you have perfectly prepared your pond. They are emerging from a long fasting season and will be hungry but weak and so their bodies are not in a condition to eat their normal diet. Begin by feeding soft and highly digestible food. You could soak some pellets with water and then feed these to your fish. But this could cloud your pond water, so take care. Alternatively source a digestible food formulated for the season and feed this once every few days to begin with. When the water temperature is consistently 55F or above, you can feed your regular koi food once each day. Consult the feeding guide of your chosen food and increase the amount you feed your fish as the water temperature rises.

Caring for Koi in Spring

With the bizarre weather which increasingly seems to afflict the UK, it can be hard to know when spring has sprung! Just when you think that the winter is behind you, another wave of snow blankets the landscape in white and temperatures plunge. But eventually spring will arrive, and your koi will begin feeding again.

The Stresses of Spring

With water temperatures going up and down like the proverbial yoyo, your koi may be feeling a little stressed! When water temperatures reach 40°F - 50°F your fish's immune system will still be on idle but harmful bacteria could be active. Keep a close eye on your stock and check for signs of distress. Any issues are best tackled as soon as possible. Check your water levels before your fish start to eat and make the necessary adjustments. A clean pond is also essential.

Clean Your Pump and Clear Your Pond

As the water temperature rises, clean your pump because when the fish start to eat, it will be crucial that your filtration system is working effectively. Leaf matter and debris may have accumulated in your pond during the winter months so pull out your pond vacuum and clear this to ensure that your pump doesn't become blocked. If you have an ultraviolet clarifier system you will need to turn it on when spring arrives. Make sure you clean your sleeve and replace the bulb!

Check Ammonia and Nitrite

It is also important to check your pond's ammonia and nitrite levels during your spring maintenance routine. As your koi's metabolisms speed up and the fish start to feed, there can be a rapid increase in toxins, a problem exacerbated by that plant matter that may have built up over the winter months. Koi pond filters take time to establish after the winter and so are initially less effective at dealing with increased biological activity. If you detect unsuitable ammonia or nitrite levels, carry out a partial water change. Remember to add a dechlorinator to your water. Ensure that dissolved oxygen levels are suitable and when the water temperature is constantly above 50°F, begin feeding your fish.

Feeding Your Koi

If you are unsure if your koi are ready for food, wait until they show signs of activity. If they are begging for food at the surface of the water, they are probably hungry and have decided for themselves that it is time to start eating! Spring can be a difficult time for your fish, particularly when the weather is doing strange things, but with good pond maintenance and careful monitoring, you are able to help smooth the transition into the warmer months.

Caring for Koi in the Summer months

As we move into the Spring and with the Summer months really just around the corner, we can all look forward to those bright and warm days which are especially lovely for Koi pond owners. The nicer weather and higher temperatures mean that it is the perfect time to be outside enjoying the beauty of your garden, your pond and the glistening colours of your fish as they dart through the water. This change in weather also comes with a few potential problems which, if you are not aware of in advance, could cause some problems for your Koi.

Reduce the temperature rise

There are a few general things that you can do to make things more comfortable for your fish. If it is possible to cast a shade over your pond with either garden accessories or plants, bushes or trees, then that would be very useful. If this is not possible then you could alternatively try to keep your water filter in the shade. It might also be advisable if temperatures do begin to soar to top up your pond with some cooler water.

Watch out for water evaporation

Throughout much of the year, the problem of evaporation will not necessarily be all that severe as temperatures and sunlight intensity will not be sufficient to merit much concern. However, when we do start to get warmer spells, it is important that you understand that water loss can be very detrimental as it reduces the size of the ecosystem in which your Koi live. In fact, over-crowding is one of the biggest causes of death when it comes to Koi. So, when things do start to heat up then simply make sure you are on hand with clean and de-chlorinated water to maintain the pond water levels.

Counteract low oxygen levels

Typically, oxygen levels tend to drop in the summer months in most types of ponds. Naturally, this can potentially be very harmful indeed for Koi and any other fish you might have, as it makes it more difficult for healthy breathing to occur. It is important to try and counteract this by introducing plenty of anaerobic bacteria into your pond. In addition, you can also take care of this problem by introducing other additives which encourage a healthier state in the water by balancing out the nitrogen cycle. Other features such as waterfalls and fountains are very useful in promoting oxygen levels by circulating water around the pond.

Algae Control

In the summer, grass has to be cut, hedges have to be trimmed and a whole host of other gardening activities have to carried out in order to keep the outdoor spaces in control and looking lovely. This however though does mean that there can be a lot of cuttings, shavings and general debris of the plants and other vegetation which has been cut back, strimmed or mown. Although in fact this debris dropping into your pond may eventually increase the oxygen levels by promoting algae growth, it is important nonetheless to keep a water skimmer ready to hand in order to clear some of this away so that the pond does not in time become completely overrun with algae.

Do Koi Carp Sleep?

It's a common question about fish in general and koi in particular. Do Koi sleep? The answer is both yes and no! humans, sleep is essential and enables the body and mind to recharge. Of course, human sleep involves relaxing until we fall into an unconscious state with our eyes closed and there are several stages of sleep for us including dreaming.

Periods of Rest

Koi do not sleep in the same way as humans. They are unable to close their eyes because they do not have eyelids and, as far as it is possible to tell, neither do they dream. Koi do require rest of course but these are a case of periods of deep rest rather than sleep as we are familiar with.

Safe Rest

Koi engage in rejuvenating periods of rest. When they are resting, koi will float in one spot in the pond for an extended period of time. They will usually choose a location in the middle of the pond or towards the bottom as this is where they will feel most safe from predators. Koi may appear not to be moving at all but will, on closer inspection, be making subtle movements to maintain their position in the water.

Sleeping Together

Koi usually choose to rest at night but if bugs are active after dark, the fish may take advantage of the opportunity to feed and then engage in some rest during the day. The fish will normally group together and sleep at the same time.

Winter Rest

Cold weather influences activity levels in koi carp. As the water cools their metabolisms slow down and they stop feeding. In extremely cold conditions the fish will enter a state of semi-hibernation and may retreat to the bottom of the pond to keep away from potential predators.

Sleeping Sickness

Whilst resting is entirely normal behaviour for koi, a listless fish could be exhibiting signs of illness. It is important to familiarise yourself with your koi's usual behaviour so you can more easily recognise any potential issues should they arise. Koi may become listless or lifeless and lie on their sides. This is often put down to sleeping sickness, which is a generic condition that can be indicative of a variety of infections. If you are in any doubt about the health of your koi carp, seek out the help of an expert in such matters. So, there you have it, do koi fish sleep? The answer is both yes and no!

When do Koi spawn?

If you keep koi then you may be keen to discover when they might begin to mate. Like people, fish can reach sexual maturity at different ages and their age can be difficult to determine.

How old are your fish?

It is hard to know how old your fish are unless you obtained them shortly after birth. Most koi will be at least one year old before they are sold. This is partly because it may take several months for them to be chosen by a new owner and offered their forever pond. You can’t base your estimate of age on the date that you purchased the koi as the information you were given may not have been accurate. To make matters worse, you can’t estimate the age of a fish based on its size. Koi vary in size naturally and their rate of growth will be influenced by their diet. You could encounter a large fish which is quite young or an older fish which is reasonably small. Breeders and specialist vets would be able to help you. There are indicators of age, but you will need the benefit of experience to interpret them. The best way to tell the age of a koi is by checking its ear bone! But you might want to leave that to the vet!

Spawning Behaviour

Koi may exhibit spawning behaviour before they reach full sexual maturity. Spawning behaviour can appear to be very aggressive and so is often confused with fighting. The courtship ritual involves the males chasing and nipping the females. This can cause the females to attempt to jump out of the pond, to hide and to wedge themselves between plants, rocks and other features in the pond. The intense nature of the activity when fish spawn may result in foamy, murky and even smelly water in the pond. Spawning typically occurs in May or June but will depend on the seasonal changes to the water temperature. You should not disrupt the pond environment by attempting to address the foamy or murky water. It is best to allow nature to take its course until spawning is over!

Finding the Eggs

When the koi have calmed down after their intense period of activity, take a look to see if there are eggs in your pond. These should be visible around the rocks and plants at the edge of the pond. The eggs will be clear, round and roughly the size of a grain of salt. Sometimes, however, the eggs are eaten by the fish.

Attending to Your Fish

After the activity dies down and the mating ritual appears to be over, it is a good idea to look at your fish to check their condition. You should ensure that they are being properly aerated, especially in very foamy conditions. Spawning is an interesting activity to witness, if sometimes a little disturbing! A few weeks later you could be lucky enough to find a host of fry swimming happily in your pond.

Keeping children safe around your koi pond

A koi pond is a fabulous feature for any garden, but those colourful fish will draw youngsters towards the water. Koi are undoubtedly beautiful and fascinating. Their wonderful patterns will be appealing to youngsters and attract them to a potentially dangerous situation. Even shallow water is a potential hazard and so children must be protected from falling into your pond.

The importance of supervision

Children should always be supervised when around your koi pond. Stay with them or remain close by and in view of the pond at all times. This will enable you to intervene at any given moment, should your child attempt to climb into the pond or appear to be at risk of falling into it. If you are unable to supervise your child continually, don’t allow them access to the garden.

Educating youngsters

Disaster could be avoided if you explain the dangers of water to your child and insist that they only ever approach the pond when you are with them. Keep reminding them of the ground rules which should include the need to ask for permission to go anywhere near the pond. Thank them or reward them when they do ask permission to see the fish.

Explain how the pond works and then ask your child questions to ensure that they have understood. The pond will initially be an almost irresistible to your little one and a mysterious place where they will want to spend time. If you unravel the mystery for them, they may be less inclined to explore on their own.

It would be wise to establish an imaginary barrier in the garden and explain to your child that they must not pass beyond that point without you by their side. This could be a tree, bush or any highly visible feature of your outside space.

Protective measures for your koi pond

If it is difficult to keep your child away from the pond for any reason, you will have to consider protective measures in the form of physical barriers. This may not be an appealing thought, as any barriers will detract from the beauty of your pond. However, they could avert a tragedy and can be removed when your child is older.

A wire fence should stop your child from accessing the pond and will at least buy you a little time if you are unable to keep an eye on your youngsters. A simple fence is relatively inexpensive to construct and can be easily removed when it is no longer required. Alternatively, you could construct an attractive wooden fence around the pond and make a feature of it by growing plants over it. An ornamental fence will be relatively costly but could become an attractive feature of your garden in its own right.

Strong mesh pond covers are also good options and will offer the additional benefit of keeping your koi safe from predators. It is possible to construct removable covers which can be placed over the pond when your child has access to the garden.

Koi ponds can be enjoyed by the whole family, but it is vital that your treasured fish don’t tempt children into the water. If you already have a pond, think carefully about how to protect children from danger. If you are considering creating a pond, make safety your first priority when evolving your design.

Why Koi benefit from natural sunlight

Most animals need natural light in order to thrive and koi certainly benefit from the sunshine. There are many ways in which sunlight will benefit your fish, but it is important to strike a good balance of light and shade. There is much to think about when caring for your koi but their need for light should never be overlooked.

Natural light and colour in koi

Natural sunlight brightens the wonderful colours of koi. This is particularly true of the Yamabuki Ogon. If a Yamabuki Ogon is kept in an indoor tank, its gorgeous golden yellow colour will inevitably begin to fade. However, that gorgeous colour will return within two months of the fish being placed in an outdoor pond. The colour of all koi will be negatively impacted if they are not exposed to sufficient amounts of light.

Koi actually look better when viewed in natural sunlight. The broad spectrum of light that the sun produces brings out the natural beauty of the different varieties of the fish.

Natural light and koi health

Koi are more likely to thrive in a pond warmed by sunlight and boasting good plant growth. Koi need vitamin D just like people but do not get this directly from sunlight as we do. The fish gain the vitamin from the plants and organisms that they eat. Vitamin D is essential for good growth and general health in koi. Vitamin D also promotes plant growth and so is vital for a creating the right pond environment for the fish to thrive.

Day and night cycles

All animals have circadian rhythms and it is important that these are not disrupted. Circadian rhythms are controlled by the natural cycle of darkness and light. It is therefore crucial to ensure that your pond is positioned in such a way that it isn’t too shady and will be exposed to natural light in the daytime. The fish need to sense the daily and seasonal changes which influence their metabolisms.

Too much of a good thing

While sunshine is generally a good thing, it can also pose a danger to your fish. Too much direct sunlight can cause your pond to overheat in the summer months and this will result in the oxygen levels in the water falling. UV radiation can present a danger to koi and so it is important that there is a shaded area for them to retreat to during the hottest and brightest periods of the day. A shaded area will also help to balance the water temperature in the summer.

You should also be aware that too much bright light over your pond can encourage excessive bacterial growth and spark algae blooms. You need to get the balance of light and shade just right to provide your fish with all of the benefits of the light and not the downsides.

It is possible to keep koi indoors, but they are better suited to life outdoors where they have the space and the natural light that promotes good health.


We are very sorry, but the browser you are visting us with is outdated and not complient with our website security.

Please upgrade your browser to a modern secure version to view our website.