When organisms such as algae become a problem in private or commercial fish ponds, copper sulfate treatment provides an inexpensive solution. However, improper application of copper sulfate can create more problems than it solves.
Excessive algae may accumulate in ponds. It may float on the surface and form a scum. Excessive algae can reduce the amount of oxygen in a pond to such an extent that fish die. Parasites such as ich may also harm pond fish.
Copper sulfate kills algae and many fish parasites on contact. It also will kill many weeds that infest a pond. Uniform spraying of a water solution of copper sulfate will guarantee that the copper sulfate spreads evenly across the pond. It is an inexpensive treatment and easy to apply.
Poisonous to Fish
Excessive application of copper sulfate will kill fish, especially if water is low in alkalinity. If a pond contains less that 50 milligrams of alkaline material per liter, a pond should not be treated with copper sulfate, according to the University of Kentucky College of Agriculture.
If copper sulfate kills a thick mat of algae at once, the decaying vegetation may deprive the pond of oxygen. For dense algal blooms, it is better to apply copper sulfate to the worst spots instead of giving the pond a complete copper sulfate treatment.