Looks like a bunch of hair algae to me. I would drip non diluted 3% peroxide on the rock / outside of the zoas. Or just soak the whole thing in 50/50 solution peroxide and water.
Hi and hello. What i would recommend is ask a more experienced person who has dealt with them before if they are what i think as ive never dealt with them so wouldnt like to advise so will tag @ vetteguy53081
It probably going to ne something like take rock out of tank and scrub off or add peroxide for few seconds
colonial hydroids. Starve them and they will be soon gone. How ? Simply direct water flow towards them, NOT at them and they will not be able to capture food and colonize