First, sorry about the lack of quality pictures but I am sure you will see what I am seeing. Tonight while staring into my reef I noticed something about my Acro I have never seen before. On the back side out of sight appeared to be a white shade on the coral. This is in a shaded area of the coral due to the branches over head. I have read horror stories on RTN. I grabbed the coral and took these pics. Please advise me what to do. Params were checked first and are as follows. Ph 8.2----normal Alk 9----normal I usually hang at 9 or 10 with little or no shifts for long periods of time Cal 420-----low I usually hang at 480. Not sure why I had the drop in Cal. I run kalk in my ATO and have done this for a long time without any issues. I did dose a little reef complete to try to bring this up. Nitrites, Nitrates, Am, Phos all undetectable. I have had this coral for about 6 months. I have seen some good growth from it. If you look closely the pictures will show the growth at the tips and even at the base spreading out over the rock. All of my other corals seem fine. I have several montis that are growing like champs and a birdsnest that is more vibrant than ever. My birdsnest I have noticed in the past has the same thing happen to it. On the bottom side of the branches near the base the coral turns white but it never appears to actually die. However, this seems different on my acro. There is no tissue what so ever on the white portion of the acro. Please help!!!!!! See the base here. This would be the back side where it is shaded. Even the new growth out across the rock has turned white. This would be the front side of the colony in perspective to the front of the tank Another shot of that spot Another Another Top view. Not a great pic sorry. But notice the new growth at the ends. Polyps are closed because of my freak out and grabbing the coral. But they have been open everyday. This is again the front side Panic setting in Lousy picture but this is the corals orientation in the tank. Notice the bottom back/right of the coral. This is shaded.