I got a GBTA from ROC 2-3 yrs ago and it has always stayed put in the same spot. Always seemed happy there. over the weekend we went to the WCR swap/bbQ and purchase an Iwasaki 15k 175 bulb that replaced an older Phoenix, I think, bulb. So the par should be higher. I raised the fixture up about 3 inches to compensate some for the extra par. My RBTA shortly started wandering to the outside walls and up towards the top. Kinda scary cause it was getting close to a powerhead. It's still up in a corner. The lighting is a 175 MH plus a little pc supplementation on a standard 50 ga tank. there seems to be a correlation between the bulb change and the wandering, although I'm surprised by it. Opinions? Other conditions haven't changed.