When algae becomes overabundant it can lower the recreational and aesthetic qualities in a pond or lake. It can also alter some of the natural pond qualities such as fish habitat. The following chemical options can be used for pond algae removal.
Sodium Carbonate Peroxyhydrate (GreenClean)
This is a fast-acting algaecide, with results noticeable within several hours in the form of algae discoloration from green to a whitish or cream color. Its mode of action is oxidation, producing 100 times its volume of oxygen as it eliminates chlorophyll in the immediate application area. It completely biodegrades into naturally occurring compounds and is non toxic to aquatic life, if used as specified by the manufacturer.
Copper Chelate (Cutrine-Plus)
Copper is also available in a chelated or buffered formulation, which is manufactured as a liquid or granule. This provides some advantages during application. The liquid form needs only to mix with water sprayed over the pond surface. There are no water-use restrictions associated with either formulation of copper chelate. Copper chelate products are less toxic to fish, but should be used cautiously in the presence of trout, koi or ornamental goldfish.
Copper Sulfate (call 800-328-9350 for price quote)
Most species of algae can be controlled with low concentrations of copper sulfate. Available in crystalline nuggets the size of rock salt or as finely ground “snow” grade. Best results are obtained by dissolving in water and spraying it directly on floating algae or injected under the water surface on submersed algae. For larger ponds, crystals can be placed in a burlap bag and towed from a boat through the water. There are no water–use restrictions with Copper Sulfate, when applied at the proper rate. Copper Sulfate is often lethal to trout, goldfish, koi and white amur. This is particularly true in soft water ponds.
Diquat Dibromide (Weedtrine-D Liquid)
This is a contact herbicide that will control lake weeds and some but not all species of Filamentous Algae. It is applied by pouring directly from the container or by diluting with water and injecting below the water surface with a sprayer. It should be applied before growth reaches the surface. Muddy water will deactivate the active ingredient.
Endothall Amine Salts (Hydrothol)
The amine salt formulation of endothall is labeled for lake weed and algae control. It is available as a liquid or granular formulation. It is a contact herbicide and is most effective in waters 65° F and above. Fish are extremely sensitive to this active ingredient. To reduce the potential for killing fish, start applications at the shoreline and move outward so that fish can escape from treated areas. There are water-use restrictions associated with endothall and liquid formulations can cause skin burns.
For complete article see:
Ohio State University, “Controlling Filamentous Algae in Ponds”, William E. Lynch Jr.