It looks like there is something irritating it's sheding it's skin and releasing slime into your water. I'd run some activated carbon if I were you to suck up any toxins that it's releasing into your water. If you have other corals they are pretty sensative but, activated carbon will remove most of the turpines from your h20.
If it's a recent introduction ," I think I remember you posting that it was", it's just adjusting to your tank. What are your water parameters, lighting and age of your tank. Uh oh, I just looked at your top pic please tell me you don't have crushed coral in a reef tank. It's going to cause you long term nitrate problems and some softies and most hard coral along with many other inverts are pretty sensative.
hth
chris