Did you google Zoa eating Nudi's? If not take a look and see if that's what you killed.
I bought a beautiful colony of Mami Vice from a member (gone now) and it had zoa eating Nudi's. I fought those nasty guys for over a year! I was NOT nice to the seller either, lol
Use a small power head in the container with the dip and blast in between the zoas (after they close) and in the pits of the rock.
They are a pain and as the post above said they lay eggs so dip the rock again in two days...
Yep that's its name...stomatta thanks! Dang 19 is a crazy lot to have on the glass at one time! I wouldn't want 19 of anything on my glass blocking my view, lol