If that is bryposis I would get it out of tank now. Toss the zoa and all. If you insist on keeping it dip for 5 minutes in 4 parts tank water 1 part h202. Your zoa won't like it and bubbles will form under the skin but it should be fine in a couple weeks. Do two treatments with 48 hours between each to be sure.
Well they happen to be Rastas so I won't toss them. My yellow tang kept it at bay in my other tank but I just downsized and no longer have the tang. So would that still be bryopsis? If he munched it?