To ensure the proper clarification of your pond water with your PondMaster UV please make sure you obtain a unit capable of clarifying the volume of water in your pond. The Pondmaster UV units are available in 10, 20, and 40 watt models capable of treating up to 6000 Gallon ponds. Multiple units may be used for larger ponds. Read all directions and make sure the pump selected to operate your UV does not exceed the maximum volume of flow for the unit. The slower the flow the more effectively your unit will operate. Too much flow will move the water too quickly thru the UV unit and the water will not have a long enough contact time with the UV bulb to sterilize the water.