Are the hydroids only on one rock?

yes, a new rock currently in qt

I have boiled the rock before with hydroids and the hydroids came back. I strongly suggest just to get rid of the rock all together. Get another one without the pest.

Curious, why not?

Fumes that can get you sick, if there are any pallies on the rock and you literally cook them, they will release toxin that can kill you. Rocks can shatter and explode if boiled and so on.

Please never never never actually cook and boil rocks.

As mentioned dont literally cook/boil rock. To kill what is on there, do bleach or acid bath. Word of warning about acid. While it does work and work fast, it can be quite dangerous to work with. So unless you know what you are doing and have all the safety gear, do a bleach bath. Takes a bit longer, but it is much safer and you get same result.

It has been a week since I added the new livestock to the aquarium. The tang was hating quarantine, it wasn't swimming and wasn't eating but looked healthy otherwise so I took the chance and put it in the display tank a couple weeks early. After a few hours of settling in it started swimming around and pecking at the rock. Now it is fat and healthy and is always cruising around looking for a snack.

The bubble tip is starting to colour up nice in its new conditions and has not moved from where I placed it. However the clowns are not interested in it and still prefer a nice bed of algae and cyano. I'm thinking they look for a specific texture for a home, and the slime on the rock does the job.

The blenny found about six different holes that it calls home, and it darts from one to the next throughout the day.

Overall everything is fat and happy.