Ahh! Ok good I have been doing furan 2 dips and coral Rx I've noticed its on only like my pink hippos and red hornets of course my favorite two zoas lol
Thats a sponge, if its growing fast remove it, if not its fine to leave
Ill edit this as I take that back, looks like bacteria, its not fungas furan 2 wouldve killed it. If its affecting the polyps by stunting its growth or not opening, i would brush/scrape or spot treat it with peroxide