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Pike County Extension Service Answers Questions About Algae

Dear County Agent

Q: I have algae in my pond. I have cooper sulfate but I have heard it is toxic to fish. Would carp be a better choice?

A: The words “slime” and “algae” can mean different things to different folks. If you have aquatic weeds in your pond, my first recommendation is to get a positive identification on the plant. Call our office and I will come out or search “aquatic weeds” on the uaex.edu website. Several resources exist to help you determine the name of the problem weed. For most algae, cooper sulfate is a good choice for control.

Cooper comes in crystal or solution form. A good starting recommendation dose rate is typically 0.5 to 1.0 ppm. To calculate a pond’s volume, multiple the acreage by the average depth. For a copper sulfate solution, mix 1 ½ lb of copper sulfate crystals with 1 gal of water. Copper can be toxic to fish, therefore, treating small areas at a time is recommended. The main problem that typically arises is the depletion of oxygen after the algae has been killed. This can lead to turn over and sequentially fish mortality. After water temperatures reach 85 degree or higher the toxicity risk increases.

Another control option is using carp. While carp can be a choice to maintain a clean pond, they will require some time to control an algae problem. After carp reach maturity, their desire to continuously feed diminishes and they should be replaced with younger fish. Using carp without herbicidal control will require one or two years for substantial control. Therefore, producers may wish to treat with copper sulfate followed by stocking with carp two or three week later. For more information about aquatic weed control refer to MP44 on the uaex.edu website or visit the Pike Co CES Office.