Easy-to use biological filter for tropical aquarium fish Aquarium filter sponge for efficient biological filtration Great biological filter for breeding or spawning aquariums Multi-strata design provides large surface area for optimum filtration. Provides the ideal location for bacterial colonization. Operated by an air pump to create numerous minute bubbles to increase dissolved oxygen content. Replaceable filter sponge allow long lasting use. Supplying the water much needed oxygen Most fit to external or top filter as prefiltration unit No deads spots in cylinder foam offers increased filtration Various types of installations are possible The sponge material is easy to clean Quiet operation Requires an airline tubing and air pump or powerhead for opeation, each sold separately.