Fish Mate Gravity Filters provide extreme 3-stage, high-performance filtration for your pond or water garden. These quality gravity bio-filters utilize coarse filter brushs to strain out debris (mechanical filtration), followed by a specially developed, profiled sponge filter that traps most of the remaining particles, finished off with a Supra biological filter media (biological filtration) section that eliminates ammonia and nitrites through beneficial bacterial activity. Multiple Fish Mate Gravity Filters can be connected in sequence for use in larger ponds. Each filter requires an appropriately sized pond pump (sold separately).