Submersible 40-watt Ultraviolet (UV) Light Pond Water Clarifier for use with pumps up to 3000 GPH, in ponds up to 6000 gallons. The 40 -watt submersible UV Light controls green water in your pond. Water can be pumped through the UV light and then into a filter (sold separately) where debris can be trapped and decomposed. The vortex flow design increases the exposure time of the water to the ultraviolet light and the slim diameter brings more of the water closer to the intense UV rays making the process more efficient. These clarifiers can be installed submerged in the pond or outside the pond. The light is submersible, so it doesn't detract from the natural pond look, and, at the same time, its slim design tucks behind pond borders for concealed above-surface installation (with proper tubing). An 18-foot power cord easily reaches nearby power sources and is UL listed. Features soft, blue indicator ring lights that show that the unit is on and working.