A truly magnificent pond filtration system, this filter is the most simple to install, clean, and maintain. The BP4000-UV is a mechanical and biological filter for ponds up to 4000 gallons. The innovative bonus to this filter is that is has an 18 watt U.V. sterilizer built in, making it a must-have for any pond or water garden enthusiast. The U.V. sterilizer will neutralize suspended algaes and other microscopic debris with the result of remarkably clear water. It also helps the spread of harmful parasites and bacterias between fish. With the turn of a switch, you can literally 'back-flush' or clean this filter, and do a water change at the same time. Using a hosing attachment on the 'back-flush' port, you can even water the garden or grass with nutrient rich pond water, with stunning results (The in-flow of water is redirected inside the filter removing the debris in your filter media and directing it out through the 'back-flush' port). This filter is a blessing for any pond or water garden enthusiast. It's easy to hide, you can literally bury two thirds of this filter in the ground, allowing for an esthetically beautiful, natural atmosphere. The BP4000-UV cannot handle more than 4500 gallons per hour. It is best used with pumps that have flow rates between 2500-4000 gallons per hour, which is recommended for the most effective back-flushing of the filter. It comes with fittings that are designed for Tetrapond's 1 1/2" and 1 1/4" no kink hosing. The construction of this filter resembles that of an army tank. Super tough locking clamps, super thick seal ring, super durable plastic canister and cover, it also comes complete with mechanical filter sponges, Bio-Activator filter media and an 18 watt U.V. bulb for the U.V. sterilizer. A wise investment for any pond hobbyist. Measures 16" in diameter, and 25" in height.