could it be bleaching from lighting installation?
I bleached an Acan back in the summer, bought the frag and put it too high in the tank. Basically, the coral was used to a low lighting intensity at the shop. What that means is that the coral regulates the density of zooxanthellae within its tissues, so the lower the light, the more zooxanthellae it needs for a steady output of sugars from photosynthesis. If lighting intensity suddenly increased, such as when I bought it, put it in my bright tank too high on the rocks (near the light), the zooxanthellae is way too high in density within the coral tissue. Not exactly sure why this irritates the corals, but it does. The balance of reciprocal exchange is out of whack. Coral provides nitrogenous wastes and carbon dioxide to zooxanthellae, and zooxanthellae provides sugars and oxygen to coral. Oxygen in high concentration can be toxic to some things. Whatever irritates the coral, the coral drastically adjusts by spitting out its zooxanthellae and deflating its tissues to minimize light exposure. I have killed Blastomusa this way. It's been since the summer for the Acan and the piece is finally regaining some colour after months of being in a shaded area.
Maybe you bleached some corals with the drastic increase in lighting, some corals died while this brain is on a slow recovery?
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