Could the issue be Brown Jelly Disease?? I've had two friends deal with this as of lately and one that brought a doctor in to examine the jelly. His conclusion was a temp swing in his tank caused the jelly bacteria to form and then wipe out all of his Acro''s over time. He said that once the jelly touched the Acro it was all over within a few days, the colony would be gone. All of his corals at first seem to brown out and STN slowly and then like clock-work it would RTN within a day or two. He was dealing with this for a while actually and finally his corals subdued to the issue and he is starting from fresh. From what both parties said is that you must completely remove the Acro and fragging doesn't save the coral. The frags would also RTN at the same time as the colony would even if it was in a separate tank. If it spreads it will eventually kill the Acro's it touches from their experience. Now, this is all what I've been told by two store owners that have been in the hobby for much longer then I have and one having an actual doctor come in and inspect the bacteria..So no one kill me if I'm wrong I'm just passing on others experience's.
Bryan