Pond Algae: Prevention and Control Methods
Veterinary & Aquatic Services Department, Drs. Foster & Smith

Q. I have a 2000-gallon koi pond that receives more than 10 hours of direct sunlight per day. Last year I experienced problems with hair algae and green water. What can I do to prevent these problems from recurring?
A. You've experienced algae problems because your pond readily offers algae the light and nutrients it requires to grow. Since you cannot feasibly move your pond to a shadier location, you must first limit the amount of nutrients in your pond, then incorporate natural algae control.

To limit the amount of nutrients in your pond, you need to stock less than 1 inch of fish per 10 gallons of water and feed only as much as your fish will consume in a few minutes. Also, test your water regularly for algae-fueling nitrates and phosphates. For residual control of phosphates, incorporate a chemical media such as PhosGuard into your filtration system. Lastly, consider installing a UV (ultraviolet) sterilizer in-line with your existing filter to help control green water.

After you've minimized nutrient levels, incorporate natural algae control into your pond. You can limit the amount of light that penetrates the water with floating plants such as water hyacinth and water lettuce. In other areas of the pond, add submersed plants such as Anacharis, Cabomba, or Hornwort. All of these plants   both floating and submersed - will compete for the same nutrients that feed algae, and will therefore help minimize algae growth. You might also consider adding lilies to help shade the pond and Japanese Trap Door Snails, which consume algae from rocks and pond decorations.

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