Yeah, sorry, but if the hydroids have been there a long time and have not become a problem, I'd say don't worry too much, as it does not solve anything especially if there is no direct issue.I know I know... but I just want a month of not having to deal with something. I plan on leaving it alone. I don't care. I'll keep an eye on my zoa and hopefully this doesn't become a problem.
Is your zoa on the rocks or on a frag plug? If it seems to be irritating the zoa, you might want to try to remove the hydroids there.