The slime, or algae, on ponds may be destroyed by copper sulfate. The common spirogyra is dispatched by 1 part of the sulfate to 25,000,000 parts of water, and other forms by a stronger solution. These weak solutions are little injurious to the higher plants and not much so to any animals. A better way is to keep the toads and to let their tadpoles eat the algae. Red-bellied minnows would also help.