[mike31154]

Well there could be other factors at play. When I started my 77 gal all I had was a Hagen GLO 36 inch T5HO fixture over it with a blue tube & a 10000K white tube. I had no coral, but a few months in I added a BTA. It survived under that light, but that was about it. I gradually upped the lighting to 48 inch T5HO & 2x250 watt Metal Halides. Then came my DIY LED fixture which consists of 27 ten watt multi-cip LEDs. That's potentially 270 watts, but I run the LEDs on a lower setting than max. Nevertheless, my BTAs are now taking over the tank & they've never looked better. The original split a number of times before I got the LEDs and the two I have remaining in the tank are huge & healthy. I hardly feed them anything anymore whereas a few years ago I was feeding small chunks of silversides about once a week. 46 watts is pretty feeble over a 90 gallon tank, whether it be LEDs, T5s or whatever. I don't think they even make a Metal Halide that small. So yeah, the LFS dude was not giving you the best advice in that regard. The LEDs on your fixture are numerous, but very small (low power) and will not penetrate the water very well. Get them as close to the surface as feasible & keep an eye on the nem while you contemplate your next move. It's probably not dying quite yet since it still has colour, but regardless of what else may be causing it problems, more light will definitely help. BTAs are one of the more forgiving nems out there.