The Helix Moving Bed Waterfall filter is like no other supplemental filter, revolutionary in its combined ease of use and incredible effectiveness! This filter is truly self-cleaning (when used as intended for biological filtration) and requires ZERO maintenance. Feed your koi for optimum growth without worrying about the waste or uneaten food. This filter can convert the dissolved and digested waste from up to 3 pounds of fish food EVERY DAY. Intended to be used with a 25 liter air pump (Not included), the Small Moving Bed Waterfall Pond Filter also dramatically increases dissolved oxygen levels in the pond, which makes it possible for koi to grow larger in less time. This product is incredible to see in action, as air and water swirl through the highly porous media. This simultaneously prevents dirt and debris build-up while creating a highly aerobic environment where beneficial bacteria can thrive and break down ammonia, nitrates, and nitrites. Can be used with a flow rate of UP TO 4000 GPH. Since this waterfall filter does not require a lid, it is easy to install and disguise in the landscape, perhaps with a faux stone or other aesthetic product. Made in America, the Small Moving Bed Waterfall Pond Filter is composed of a heavy-duty roto-molded body, stainless steel hardware, and high quality plumbing parts. This filter includes 15 liters of Helix floating filter media, a 5" Radial Air Diffuser, a 3/4" pre-drilled bulkhead, and a 2" pre-drilled bulkhead with 2" suction strainer to protect from debris. The product dimensions are 19" L x 18" W x 35" H. NOT to be used as stand-alone filter as it does not have any particle filtration. Helix makes four kinds of waterfall filters: the Static Filter, the Biomechanical Waterfall Filter, the Biomechanical Reactor, and the Moving Bed Waterfall Filter.