We bought a Coralife UV and used it near the beginning of our 55. We had been having problems with ich (QT tank seemed to be more of a problem than a help...still don't know why). We had been losing fish in our tank for a few weeks, then started running our sterilizer and haven't lost any fish since (KNOCKING ON WOOD). I have since turned off the sterilizer, as we have added corals to the tank, and I have been told that the sterilizer will kill not only detrimental critters but also the things that many corals eat. I still have the sterilizer in the tank (there just in case things go wrong).