Algreen PressureFlo 4000 Mechanical and Biological Filtration for Ponds/Fountains/Water Features and Gardening Mechanical and Biological Filtration helps maintain clean and healthy pond water Integral Ultra-Violet sterilizing clarifier permanently and continuously controls algae Ideal For water filtration and cleaning of large ponds up to 4000 gallons Includes In/Out valves for simple and quick cleaning Reduces maintenance of your pond Includes 2 year warranty and is U.L listed