2 BRAND NEW FILTERS Sponge filters provide both mechanical and biological filtration. Simply install an air pump into the unit and provide both aeration and filtration for your fish. Aerobic bacteria colonize the sponge providing a bacterial substance to facilitate the nitrogen cycle The sponge traps larger waste particles mechanically cleaning the water without trapping baby fish They are useful for breeding filter or secondary filter. They also can be used as pre-filtration unit by fitting to an external or a top filter Easy to clean, simply rinse and squeeze sponge under cool running water