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How to Tackle Algae In Your Pond



There are over 17,000 different species of algae. Some species are beneficial but ponds can be afflicted by non-beneficial species including plankton algae and filamentous algae.

The Causes of Excess Algae


Algae requires nitrogen, phosphorus and sunlight to grow. Stocking your pond with too many fish or overfeeding your fish will result in too much waste being deposited in the water and this will then rot. The rotting process fills the water with the nitrates that the algae thrive on. Decaying organic matter such as leaves will have the same effect. Lawn fertilisers that run off into the water will also feed the algae.

The changing seasons can cause algae to bloom. In the spring, the beneficial bacteria have only just begun to multiply and plant coverage will not have fully developed. This situation, accompanied by the increasing temperatures, could result in excessive algae forming.

New ponds need time to balance. They should not be stocked with fish until sufficient beneficial bacteria have developed. Algae may form on the shallow edges of any pond where the water is warmer and circulation is limited.

Non-Chemical Algae Treatments Including Pond Filters and Pumps


You should rake out all algae that you can reach. Add plants that will compete with the algae for the available nutrients and shade some of the surface of the pond with water lilies. Ensure that you have the correct biological pond filter for the size of your pond and that your pond pump will turn over the total volume of water every two hours. It will also help if you vacuum the bottom of the pond regularly. If necessary, add nitrifying bacteria and a place for the bacteria to grow, such as rocks.

[caption id="attachment_105" align="aligncenter" width="500"] Algae by Alex Quinn via ()[/caption]

If the edges of your pond are affected by algae, address the movement of water to ensure that circulation is improved at the pond's margins. Remove all debris and dead leaves manually or with a skimmer. It may also help to add an organic pond water colourant to keep out the sunlight.

What Not to Do


Don't replace any of your pond’s water with tap water (see on why). This will increase the nitrates in the pond and could kill beneficial bacteria. Also, never change all of your pond's water at once as this will result in an algae bloom. You should only ever perform partial water changes using collected rainwater or well water.

An ultraviolet (UV) clarifier will destroy floating algae but should not be used unless you have zero ammonia. A UV clarifier will not help with string algae.

Do not over feed your fish or keep more fish stocks than your pond can comfortably support. One 6" fish per every 100 gallons is appropriate. Feature no more fish than can fit nose to tail across widest portion of your pond.

Little and Often


If you keep a close eye on your pond and react to potential issues as they arise you should be able to keep troublesome algae at bay. A little effort every so often will prevent you from facing a major project further down the line!

At Krafty Koi we have a great in stock from top brands such as Blagdon, Tetra Pond and Evolution Aqua, all of which have been especially designed to help you bust any blooms.

  • Header photo: Algae by  via Flickr ()

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