Algae Management for Koi Ponds and Water Gardens

Here we describe 3 scenarios and possible algae management plans for Koi ponds and water gardens that you can use to maintain or improve water quality. Please realize that every pond is different, and strategies should be adjusted as conditions change. So, you should use these basic strategies as a reference or example, not as a strict plan to follow regardless of the situation.

Also, these techniques can and do impact oxygen levels in ponds. Even ponds with waterfalls can experience oxygen depletion under extreme conditions, such as very heavy algae growth. Be sure to always read and follow product label instructions when applying these products.

Brand New Koi Pond or Water Garden

    1. Control external nutrient loading. For example, be sure that when it rains, no water runs-off into the pond, bringing dirt and fertilizer with it. Also, keep leaves, grass clippings, mulch, soil from plant pots & bird droppings out of pond water as much as possible.
    2. Apply a Water Conditioner to neutralize Chlorine, Chloramines & Heavy Metals, and a liquid Pond Bacteria to seed the Biological Filter as directed.
    3. Install a properly sized Aeration System especially if you do not have a significant waterfall that runs continuously.
    4. Apply Algaefix as directed if you experience nuisance algae growth (nuisance means more algae than what you want...all ponds have some algae). Warning! – Decaying algae can lead to an oxygen depletion, which can cause fish kills. Always read and follow product label.
    5. If you do an algae treatment, apply a Phosphorous Binder/Remover as directed when the algae has died back. This will lock up the nutrients released from the decaying algae.
    6. Reapply the algaecide as directed whenever the algae starts to regrow.
    7. We like to switch from Liquid Bacteria to Dry Bacteria (for example, Easypro Sludge Remover Bacteria) in the summer when things have stabilized. This is because the biofilter of the pond is in full swing by then, and a bigger issue is build-up of organic debris on the pond bottom, which the dry bacteria will help with.
    8. Perform a 10% water change once a month by pumping or draining pond water out of the pond, applying 1/10th of the initial dose of the Water Conditioner to the pond, and refilling. This can be most easily and effectively accomplished by using a pond vacuum.


Green Water in Koi Pond or Water Garden

    1. This commonly occurs in new ponds, ponds that have just been started up in the spring, and in ponds that have received an overload of nutrients, like overfeeding fish, or dirt running off into the pond. As long as you have greater than 18 to 24 inches of water clarity, we recommend that you follow the “New Pond Program” described above, and not worry about the green tint. In a properly designed pond, the color should dissipate within a month or so as the Biological Filter becomes active. However, if water quality gets worse, go on to #2.
    2. Verify that excess nutrients are not getting into your water
    3. Verify that you are not overfeeding your fish
    4. Verify that your pump is moving the entire water volume of the pond through your filter at least once every two hours, but preferably once an hour, and that your filter is properly sized for your pond.
    5. If water visibility is less than 18”, perform water changes treating make-up water with a Water Conditioner until clarity is improved. Be sure not to drop your water temperature by more than 5 degrees F in 24 hours, as this is very hard on fish and plants.
    6. Apply Phosclear Phosphorous Remover as directed until water has cleared (usually clears in 3 or 4 applications, unless there are major issues).
    7. Add Water Lilies or other plants or structures to help shade the water from the sun.


String Algae Growth in Koi Ponds or Water Gardens

    1. Verify that excess nutrients are not getting into your water
    2. Verify that your pump is moving the entire water volume of the pond through your filter at least once every two hours, but preferably once an hour and that your filter is properly sized for your pond.
    3. Physically remove any heavy mats of algae that are easily accessible.
    4. Aerate water as much as possible by running pump and waterfall 24 hours a day. Serious algae problems may require Supplemental Aeration to prevent oxygen depletion during and after the following treatment.
    5. Apply 3.3 ounces of Algaefix per 1,000 gallons of pond water every 3 days until all algae is dead (usually takes 1 or 2 applications).
    6. After algae has died and started to decompose, apply a Phosphorous Binder/Remover as directed. The Phosphate Binder/Remover chemically binds up most of the remaining nutrients and precipitates them out of the water in a form that algae cannot use.
    7. If algae begins to re-grow, repeat 5 & 6.