How Much Copper Sulfate in Ponds?

Pond Alkalinity

• The critical measure required is the water alkalinity. This is different from the pH balance, and is noted as the parts per million (ppm) of the water. A test chemical is dropped into a sample of pond water, which then turns the water blue. The amount of blue test water required to turn another chemical pink then gives the measure of alkalinity. Ponds should have a reading of 100 ppm, with an acceptable range of 50 to 200.

Working Formula

• Divide the alkalinity ppm reading by 100 to find the amount of copper sulfate to use. For example, if the ppm is 200, then you would use 2 milligrams of copper sulfate per liter of pond water. Do not use copper sulfate if the alkalinity ppm is under 50 as this will likely kill the fish. Do not use more than 2.5 milligrams of copper sulfate per liter of pond water. The University of Kentucky recommends using 2 lbs. of copper sulfate per acre of water with a 100 ppm reading, and 5.5 lbs. per acre with a 200 ppm reading.

Dispersal Technique

• Copper sulfate readily dissolves with water, and it should be watered down as much as possible before adding it to the pond. Otherwise it will sink to the bottom and bind with the chemicals in the soil. Adding it unevenly to the water will create spots that are toxic to the pond life. If there is a large amount of algae with little air circulation in the water the University of Florida recommends that copper sulfate not be used.

Alternatives

• Due to the toxicity of copper sulfate other alternatives have been developed. Effective algaecides using a modified form of copper sulfate that is not as toxic are available for ponds. Cutrine-Plus and Captain Algaecide are more expensive to purchase than copper sulfate, but their effects last longer and less is needed over time.