I use one in my system. It helped control an ich outbreak. I have unplugged the uv to see the effect it would have in my tank. I unplugged it for a week. My water was not as clear and my Powder Blue Tang and Lyretail Anthias were going to my cleaner shrimp more often to get cleaned. I also noticed them scratching on the sand. My temp also dropped by 1 degree. After I plugged in the UV my water was crystal clear again, the fish stop scratching, and my fish stopped going by the cleaning station. Temp also increased 1 degree. After seeing the positive effects it had in my tank, I decided to keep using it.