Its probably too late because it sounds like its starving to death. They require strong lighting(MH), only the best water conditions(no nitrates or phosphates) and daily doses of Marine Snow or DT's Phytoplankton(possible option). They are considered to demanding to maintain by the average reef keeper.
If the above conditions can be rapidly solved it may be possible to save it by cutting away all affected branches before it disintergrates completely.
BurnNSpy