Rena Filstar Foam 20API 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 filters Open cell design allows free flow of water without clogging Removes suspended debris