Aquael PhosMAX is a powerful, effective filter media made of a specialized form of grit with highly absorptive properties, with the purpose of eliminating toxic phosphate ions that cause unsightly algae buildups. However, the media works selectively, taking only the negative elements in the water and leaving beneficial nutrients and minerals. The versatile filter media is well suited for freshwater aquariums and terrarium pools. PhosMAX is made up of a crushed grit that allows for the flow of water between pieces, and can be used effectively in canister filters, sumps, overflow filters and internal filters. The media is ideal for aquariums with large quantities of fish eating meat based foods, such as catfish and cichlids, or aquariums without plants, as plants act as a natural phosphate absorbent. It is completely safe for all fish and plants, and provides unmatched chemical filtration to keep your aquatic habitat healthy and clean. To maintain optimal function, the media should be placed after both the mechanical filtration and the chemical filtration, and should be changed every 4 weeks.