Submersible 40 watt Ultraviolet (UV) Light Pond Water Clarifier for use with pumps up to 3000 GPH, in ponds up to 6000 gallons. Kills suspended algae with UV light. Water can be pumped through the UV light and then into a biological filter (sold separately) where debris and dead algae can be trapped and decomposed. When installed correctly, UV lights are very effective at eliminating green water pond problems. This UV light has a 3/4 barbed intake and outlet for flexible tubing and is equipped with an 18 ft power cord. The soft blue halo light rings show that the unit is working. The vortex flow design increases the exposure time of the water with 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 submersed in the pond or outside the pond. UL listed."