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Using copper sulfate in ponds

Copper has been used for many years for effective control of algae in farm ponds and in aquaculture operations.

However, when using copper, pond owners should be aware there is only a thin line that separates effective algae-treatment levels from lethal overdoses to fish. This is why managers need to know when and how to use copper in aquatic systems and what precautions to take before using it.

Copper can be used to control pond algae, including filamentous algae such as Spirogyra spp., Pithophora spp., Cladophora spp. and the higher algae Chara and Nitella.

Copper comes in several readily water soluble forms, the cheapest and most commonly used is copper sulfate. This form of copper is available as a crystal or powder and is known as “bluestone” or “powder blue.” When copper sulfate is bought from a commercial manufacturer of copper, the percentage of copper in the formula should be carefully noted.

Several companies market copper in chelated liquid and crystal forms.

Chelated copper compounds stay in solution longer than copper sulfate does, tend to control algae better and are safer to fish. Chelated compounds do have higher initial costs than copper sulfate does. Dosage rates of copper compounds depend upon both manufacturers’ instructions and chemical types.

Dosage rates must be determined before any type of copper treatment can be used.

The first step before using copper is to measure the total alkalinity of the pond water in ppm or parts per million and the pH. This is important since the toxicity of copper to fish increases as the total alkalinity and pH decrease. If total alkalinity is less than 40 ppm, copper treatments are not recommended because of the risk to fish.

Gary Burtle, University of Georgia aquaculture specialist said, “Alkalinity is the ability of water to neutralize an acid and is based on the number of calcium ions in the water column. When using copper compounds in ponds with alkalinity readings below 40 ppm there is a greater chance that copper will be toxic to fish. At these lower alkalinity levels copper can precipitate out of the water column onto the gills of the fish and this is where the damage occurs.”

When applying copper the volume of water should be determined and the compound carefully weighed out and then thoroughly dissolved in water.

Copper sulfate is much heavier than water, and if crystals or powder is simply thrown into the pond, it will sink to the bottom and will be bound up in the bottom sediments. Copper sulfate should be as diluted as much as possible and great care should be taken when applying it to the pond surface to prevent hot spots from occurring.

Copper treatments are very effective algaecides and are inexpensive compared with other types of chemical treatments. However, caution must be used when applying copper because of its potential harmful effects to fish and other aquatic life. If your pond water is low in alkalinity, pH or if you have a heavy algae bloom and no aeration, copper treatments should not be considered.