Help my bta is bleaching

I have had this BTA for about 3-4 months. When I first introduced it to the tank it stayed in the back behind the rocks until it made its way up the to the rim of the tank just on top of one of my powerheads where it wasn't receiving the best lighting. That's where it stayed and I figured it was fine since it was staying in the same place. Weeks later it begins to shrink in size, deflates, and begins to loose color. Since it wasn't moving itself, I gently moved it to a brighter spot where there was also more water flow. It settled down in a rock full of zoas and looked much happy for several days. But now it has lost all color and is not nearly the same size when I bought it. The mouth looks fine and I feed it every other week or so.

What am I doing wrong? Too much flow, not enough? Lighting? Should I be supplementing?

Any response would be greatly appreciated!!!!

Thanks