For ponds up to 6,000 gallons as a clarifier (algae) and for ponds up to 2,000 gallons as a sterilizer (bacteria)Glowing monitor halo ring, visible from any angle, immediately shows it's working (notice the green ring around the units in the picture)40 watt UV lampSubmersible or in lineConnections: 1-1/2" barb inlet/outletA pump is a required. The required flow rates:-Clarifier (algae): 1,700-2,300 gph-Sterilizer (bacteria): 900-1,150 gphDimensions: 25" X 4"Ballast separate from unitIncludes transformer and 18' grounded power cordBlack color is unobtrusive whether used in or out of the water