The Penn Plax Cascade 500/350 GPH Canister Filter Aquarium Bio Sponge keeps the water in your aquarium clean and clear. This Cascade filter sponge removes ammonia and nitrites from the water keeping your fish tank healthy; clean; and odor free. This bio sponge also optimizes the colonization of beneficial which prevents cloudy water and excess CO2 which can harm. Made specifically to fit the Cascade 500 Standard and Elite Canister Aquarium Canister Filters; this replacement bio sponge fits securely without gaps that lead to weaknesses in filtration strength. An exact fit keeps debris and contaminants from getting through your filtration system and back into water. Made of a durable poly-fiber; this bio sponge filter is made to last for several months under normal conditions. When used together; the Cascade 500 Filter Model CCF1UL and Cascade 500 filter cartridges provide maximum protection against water pollutants from harming your fish.