Crystal Blue Copper Sulfate controls mose species of algae with very low concentrations of copper sulfate. Copper Sulfate treatment is more effective when used in water that is 60 degrees or above. Works by direct contact with algae. Lowers the oxygen level of your pond which may harm your fish if you do not have proper aeration. For Algae Control, mix 2.5 - 4 pounds per acre foot of water over 60 degrees. NOTE: treat half the pond, wait 10 days, treat other half - since copper sulfate depleates oxygen supply.