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 requiredr r as water is pumped through the clarifier the single celled algae are exposed to high levels of uvc radiation emitted from a uv lampthis uv exposure destroys the algae cells which are then broken down by bacterial a