i agree with the above post...I have a 36watt CSL on my 60g tank with a rio800 for the flow. I am just starting to add corals to the tank. I also used a 9watt UV on my old 29g for the first 5-6 months.
one thing is that you must have the right flow rate otherwise the UV is worthless. You must have the correct emposure to the light. Another is that it helps kill free floating algea and bacteria and parasites. The problem is that it kills indiscriminatly. the bad and the good are killed. IMO its great to use the UV for the first 6 months on any SW tank. After that it should be taken off, hopefully the system will stablize w/o it. But by no means are UV's mandatory. They are one of those things that are in the discrestion of the hobbyist.