IF it is bryopsis, I've read lots of posts that tout Flucanozole as the go to treatment for it. I'd research it more to make sure it won't take out all your other algae, as this could have negative effects on the other algae in the tank, thus effecting you CUC. Look on this forum for more info. I've been lucky so far and not had to deal with this particular issue. Before u do anything u need to confirm that this is what ur dealing with. A better pic will help with confirmation.