Penn Plax Cascade 500/350 GPH Aquarium Canister Filter Bio Sponge Replacement Keep your water clean and clear with the replacement bio sponge for use in the Cascade 500 Model CCF1UL and Cascade Elite canister filter models. The bio sponge filter removes ammonia and nitrites from your aquarium tank keeping your aquarium clean; healthy; and odor free. Filter sponge optimizes the colonization of beneficial aerobic bacteria which prevents the water from becoming cloudy and harming fish. Perfectly cut to fit into the Cascade 500 filter tray without any gaps which could allow pollutants to re-enter the water. Genuine Penn Plax replacement cartridge for Cascade 500 models. When used together; the filter and bio sponge provide maximum protection against water pollutants.