The Fluval Moss Ball helps create ideal aquarium conditions for small fish and shrimp by adsorbing and trapping phosphate and nitrite. It also helps reduce aquarium maintenance by deterring the growth of many compounds that cause the unsightly buildup of organic matter. The Fluval Moss Ball also serves as an attractive decorative addition to aquariums. Designed for freshwater shrimp or fish aquariums, it is effective for up to 2 months and treats 10 to 20 gallon aquariums.