Algae resemble a green rash and must not be allowed to grow in excessive amounts as they can prove toxic to other forms of aquatic life. Algaecide and products such as Algae Destroyer keep the algae growth under control. Barley straw bales are another common form of algae control because they are safe on fish and other aquatic plants. Barley straw bales contain a mixture of barley straw and microorganisms that inhabit algae from blooming. The adequate amount of barley straw bales to service a 2,000-gallon pond costs approximately $30; while barley straw for a 20,000-gallon pond costs about $100. UV Clarifiers or UV Sterilizers are also popular methods of algae control. These are installed between the pump and the filter and can eliminate up to 99 percent of a pond's algae.