Canister filter media designed to fit the FilStar XP. Aquarium Pharmaceuticals Rena Filstar Foam removes coarse debris and solid wastes before they enter chemical and biological filtration chambers.Rena Filstar Foam 20 and Filstar Foam 30 are sold separately!The Filstar Foam 30 Filtration system can be used for removal of fine debris in aquarium. To use, place Foam in the lowest part of the bottom basket in filter, above Filstar Foam 20. Rinse every two to four weeks to maintain water filtration.Be sure to replace after several months. Can be rinsed and re-used many times. Open-cell design permits free flow of water. There are two pads per box!Specifications:Foam 20 - (20 ppi - pores per inch)Foam 30 - (30 ppi - pores per inch)