Blastomussa receding tissue

[Delphinus]

Yeah I wouldn't guess any of those fish to be suspect in this case. Just thought I'd ask though, because in the past I had similar issues with blastos, and it was naughty fish in my case. Good luck getting it sorted. My thinking on this is that it can come around, try feeding the Acan+ as suggested, it does seem to help them out if they're hungry. With that said I don't target feed mine, but on the flipside, maybe I have a dirty overfed tank