I have an AquaTop 400 canister filter on my 75 gallon tank which is equipped with a UV chamber. I'd never used it, I bought the filter because I liked it for other reasons. But a couple of weeks ago I suddenly had an algae bloom in my tank that really clouded my water. I turned the UV light on and the tank was cleared in a little over a day. It really works. I shut it back off though because I've read they can sometimes melt the walls of the filter chamber.