Penn Plax Cascade 700/1000 GPH Bio Sponge (4-Pack) Pack of 4 Penn Plax Cascade 700/1000 GPH Bio Sponge Keep your water clean and clear with the replacement bio sponge for use in the Cascade 700 Model CCF2UL and Cascade 1000 Model CCF3UL canister filters. 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 700 / 1000 filter tray without any gaps which could allow pollutants to re-enter the water.