In my opinion, a UV clarifier is an indispensible partner for a good pond filter. Unfortunately I am often confronted with dangerous half truths about this subject. First of all we need to say that the operating principle is the same or similar for every make. Filtered pond water in an enclosed housing flows past a UVC bulb. During this process bacteria and algae spores are so heavily damaged that they die. Contrary to widespread belief this does not make the pond germ-free. The bacterial count is, however, significantly reduced by non-stop operation. The effective period of a UV bulb is limited to a maximum of one season. At this point the question arises whether it kills off all bacteria or it can distinguish between good and bad bacteria. Of course it can’t do that. It eliminates the free floating bacteria and germs, but not those which are bound to the substrate. This means that all the bacteria that live in the sludge and filter are unaffected and can carry out their work.