TetraPond?? GreenFree????UV Clarifiers provide permanent control of suspended algae which cause green water. Heavy green water algae blooms are removed in most ponds within 5 days, keeping the pond green water algae algae free. This means water clarity is improved while reducing pond maintenance. Each unit is compact, durable, easy-to-install and energy efficient. This UV Clarifier is not submersible and should be brought in during the winter months when temperatures are at or below freezing. It is very important you follow installation instructions in order to ensure you do not run too many GPH through this unit. These are the newest model of Tetra???s Green Free UV units. Info from AZPonds