Use the Blagdon Minipond Water Garden Green Water UV Clarifier MPU4500 UVC 5w for effective long term control of green water. The UV Light lamp kills green water algae, this is a chemical free solution that produces no detrimental effects to the environment or water quality. It works by drawing the algae into clumps so that it can be picked up by the filter system. With a 5w power consumption it is economical to run and is also safe and simple to install. It comes complete with a weatherpooof low voltage transformer and is effective in conjunction with all filter systems. Specifically designed for outdoor use. It can be used with any in-pool or external filter for effective control of green water.