[Brian317]

I have mine 3-4" away I believe on the rack. Like Doug said, if too much heat is getting to the tanks, you can blow the heat away from the lights with a fan so the tanks don't get too hot.
Bryan

Yeah, I may have to rig up a fan on mine for the summer, but I'm about to test and play around with the heat difference(if any) between 2 T5HO's, 2 normal T5's and variations. I thought the 54watts per for the HO's would produce more heat from the fixture/lights then the 26watt normal 6500K bulbs...I've also thought about lifting up the fixture a couple more inches, (sitting 2" off) but with the zoomed HO fixture, you "screw" it on the side of the tank...hmm

Sorry to get off on a rant haha, but maybe you have the same questions/concerns as me. I agree with the above posts, I think if you are/worried about having heat issues, raising the fixture up a few inches or a small fan blowing air across the top would be the best options. Best of luck.