I believe that is them expelling excess zooxanthella. Mine does it from time to time. I dont think its anything to worry about, just kind of strange looking.
No recent changes. Ammonia=0 nitrite=0 nitrate=20 salinity=1.023 temp=~79 calcium=380(trying to get it higher). I know the lighting is sufficient. It looks fine and Im not worried about it, just curious if anyone had experienced this before.