I have an LPS brain coral in my tank. For several months it was doing great. IT would baloon up during the day and go back down at night. Just about a week or so I noticed it expelling some brown stuff, and again tonight I noticed it again. Seems to be expelled from the three 'mouths' on the coral. I am rigorous on my water changes and recently tested. Everything looks good. Nitrates - 1ppm Nitrites - 0 Ammonia - 0 pH 8.3 dkH - 7.62 Calcium - 450 Magnesium - 1100 I know alkalinity is a bit low, and have been playing with the time on my dosing pump to get it at a consistent level. I'm running carbon and GFO. Carbon gets replaced every week, and the GFO gets replaced when I notice a change in the algae on the glass, which is typically every two weeks or so. Photo of it expelling the brown stuff. Photo of how it used to look. I tried to include the photos, but they were too large, had to link instead. All of the other corals seem to be doing great. My neon green candycane is getting to the point where some of the heads are starting to split. My xenias have split once already and are growing great, The RBTA has been growing continuously, my cleaner shrimp just molted for the 4th time, everything else is doing awesome from what I can tell. Only thing I can think it 'might' be is that I switched GFO (switched from BRS high capacity to Coral Vue GFO to save a bit of money) and this new GFO is virtually impossible to keep fines from circulating through. Its a very soft GFO and IMHO is JUNK! Whatever the opposite of recommend highly is what I would do for that GFO. One other thing I did was switch out my bulbs on my T5s. Initially I had (all HO): - 1 420/460k - 3 10000k - 2 Antic Switched to: - 4 ATI Blue - 1 ATI Purple - 1 ATI Coral Any help would be appreciated.