It’s simply mucous. The coral is irritated. Not mesenterial filaments either, those will look like tiny coiled white strands and come out of the polyps mouth. Mesenterial filaments will also not detach with flow, that’s a conclusive test to check. Polyps will extend and actively grab food if it’s actually eating. years ago when I fed with the real deal frozen cyclopeeze i could feed a whole tank and witness corals actually catch and swallow food. Zero sliming as shown above. I have yet to find a replacement food that works as well and I have tried nearly everything commercially available. Only thing that comes close is fish eggs from fresh fish that I catch myself in the gulf.
