Tetra Pond Bio-Active Pressure Filter with UV Clarifier BP4000-UV is designed for ponds up to 4000 gallons. Bio-Active Pressure Filters provide mechanical and biological filtration to help maintain clear and healthy pond water. Its unique open profile bio-activators provide large surface area and unrestriced water flow to all surfaces for improved cleaning. It is designed with an easy, backflush valve for fast cleaning. This filter also integrates an Ultra-Violet Clarifier that provides permanent control of suspended algae which cause green water. UL listed and includes a 2 year limited warranty (excludes bulbs).