Green water, caused by millions of suspended microscopic algae, is the curse of many pond keepers, so what is the best way to control this nuisance? A good quality pump, filter and ultra-violet clarifier system, of a capacity to suit the size of the pond is all that is required. As water is pumped through the clarifier, the single-celled algae are exposed to high levels of UVC radiation emitted from a UV Lamp.This UV exposure destroys the algae cells, which are then broken down by bacterial action in the filter. The UV output of the lamps degrades with time, and so they will need replacing periodically. Unlike many other brands the Arcadia range of \'Ultra Clear\' UVC lamps, will perform constantly for a 12 month period - ONE YEAR - ONE LAMP.