The JBJ Bio Aquarium Filter Cartridge is a complete four-stage replacement filter cartridge for the JBJ Internal Bio Filter (sold separately). The coarse sponge and filter floss in this cartridge provide mechanical filtration， trapping free-floating detritus to keep your aquarium water crystal clear. For biological filtration， the sponge and the ceramic rings have coarse and porous surfaces that allow ammonia and nitrate-removing beneficial bacteria to grow. The activated carbon provides chemical filtration， absorbing impurities and removing odors and discoloration. The filter cartridge fits perfectly in the JBJ Internal Corner filter (sold separately)， and switching it out is as easy as can be. Simply slide out the old cartridge and replace it， then you’re done!