API Rena Filstar XP Filter Foam is a Stage 1 mechanical filtration media that removes coarse debris and solid wastes before they enter the chemical and biological filtration chambers. Filtration Foam helps remove suspended debris, ammonia, medications, dyes, and other contaminants from your aquarium water. Mechanical filtration media for Filstar XP canister filtersOpen cell design allows free flow of water without cloggingRemoves suspended debris and harmful chemicalsInstalls easily and helps reduce aquarium maintenance30 PPI (Pores Per Inch) pads provide finer filtration for removal of smaller debris, and may be used in conjunction with 20 PPI pads. To use, place 30 PPI pad in the lowest part of the bottom basket in the filter, above 20 PPI pad. Rinse every 2-4 weeks and replace every 3 months for optimal filtration.