The Aqua Ultraviolet Classic 25 Watt White 2" UV Sterilizer is the premium choice as a clarifier and sterilizer in ponds and aquariums. Used as a sterilizer, the Classic 25 Watt UV is the premium choice for a 500-1200 gallon pond or an aquarium up to 150 gallons. Used as a clarifier, the Classic 25 Watt can treat up to 4000 gallons of fresh water that has 50% to 75% plant coverage. A pump is a required. Max Flow For Ponds: 2000 gph as clarifier, 1200 gph as sterilizer. The recommended flow rate for aquariums for algae is 332-554 gph and for protozoa is 110-184 gph. Dimensions: 20" X 6" X 2-1/2"Inlet: 2 slip, Outlet: 2 slipWhiteHousing: Limited lifetime warranty on housing against Ultraviolet degradation. Complete Unit: One year from date of purchase or 18 months from manufacturing dateControls algae, bacteria & protozoaClears water in 3-5 days, sometimes overnight Instructional Manual (pdf format in new window)