Thanks Mike, I read that article and it seemed to ambiguous so I figured I would see what the populous had to say.I had one for ten years. It broke about a yr ago and I just decided to go with out it from now on. It`s OK for parasites or algea spores but it only kills what goes through the lighted chamber. Anything that stays down near the substrate is not going to feel the effects. We have an article about UV lights in our articles section.