Blastomussa receding tissue

[RESONANCE]

Not sure if this helps...is your water really clean? The reason I ask is that I've read blastos also come from turbid waters, so they tend to like things on the dirty side. I've also heard from people who tried keeping blastos in their clean water sps systems, blastos never last very long for them.

Also any chance your hermit crabs or some other critter like a fish may be picking on the blasto's mantle? When ever I see damaged tissue on a blasto I do a quick lugols dip to try and stave off infection and hope for the best.