An evaporation pan must be cleaned frequently to keep it free from sediment, algae, and oil films. Any of these contaminants will materially affect the rate of evaporation.

The growth of algae can be discouraged by adding a small amount of copper sulfate to the water. (Approx 5-10 mg of copper sulfate per liter of water.) A standard Class A pan filled to 8 inches would require about 1/2 teaspoon of copper sulfate granules.

If algae is already present, it must be removed first by thoroughly cleaning the pan. Dry granules added directly into the pan will sink to the bottom and may not dissolve completely. If you have this problem, the granules can be dissolved in water before being added to the pan or placed in a burlap bag and dragged around the pan until dissolved.

It's not necessary to add additional copper sulfate each time you add water to the pan. The copper sulfate doesn't evaporate with the water but remains in the pan.

Copper sulfate is corrosive and can be toxic to animals and fish, so it must be handled with care and disposed of properly. Copper sulfate can be purchased at feed and agricultural supply stores, garden centers, and pet supply stores.