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-violetclarifier 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 destroysb 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 weill need replacing periodically. Unlike many other brands the Arcadia range of \'Ultra Clear\' UVC lamps, will perform contstantly for a 12 month period - ONE YEAR - ONE LAMP.