Hi all, I recently got a frag of zoas and they were great for about 2 weeks. Fast forward another two weeks and they now seem to have this fine grain like sand on their soft tissue (pictures below). I have tried to scrub it a little and it's quite hard. They have been closed for about two weeks now. The other zoas in my tank look great. I have tried to treat with sea chem iodine 3 times in the last week but I don't believe it's helped. If anyone has ideas on what this might be I'd appreciate the input. Thanks!