I think your parameters are pretty good,maybe temp could be a smig lower but I dont think thats causing your problem.I have a book here on corals.it say "When distured the polyps cotract and the colony blanches white"I would say the fish or something else is bothering it,maybe try to move it.I dont think it is too far gone yet.It can recoperate if you can stop the agression against it.Keep us posted