I also made this topic in the reef section as well. As you know there is a lot more action over there, so thats why i did so. This is basically what my bottom line is;
http://www.drsfostersmith.com/product/prod_display.cfm?c=3578+4393+7999&pcatid=7999
"I bought one of these, the 36Wunit for my 70 gallon tank. The water makes more than 1 pass as opposed to units that run the water straight through. I'm in the process of buying a flow meter so that I can set it to around 400gph. Yea, I do have the water being pumped back into the sump. If it was hooked up to my return pump, my rate would be way to fast and the exposure time wouldn't be as effective, but of course that's my opinion. I have no disease in the tank, but I think it would help if I brought parasites in from a new fish.. It seems to me that a unit this size in my 70 gallon tank could make a difference. The actual # of gallons may be someplace around 50 something, when he water displacement taken up by my fake coral and crushed coral substrate"