Dying millipora

[B.C.theReefer]

I have had a A.millipora for about two months now. At first it very well in my tank. It actually gained color and the polyps extended further than they did at the store I purchased it at. After my most recent water change it started losing tissue at the base quite rapidly. At the same time my powder brown tang, for lack of a better term, started geeking out. He's running into the rocks and is breathing heavy. I'm religeous about testing my water parameters and doing water changes. Everything appears fine. I'm pulling my hair out trying to identify the problem. Any help would be appreciated.

[Pmolan]

It could be a coincedence but I would start looking at whatever you used that could have contaminated the new water.