Brown Hydroids

[hillegom]

I have had those. I agree, they are a pita to remove.
Also tried the fire trick. Took rock out and burned them with a propane torch. This never killed them all, would always come back. I think too much water in the rock keeps the roots alive,
I also got rid of the rock, dried it out, and its still dry, not knowing what to do with it.
I had another rock that had 3 hydroids on it. I took a large syringe, one about an inch in diameter, and filled it with boiling water. I had to do that about 3 times and they never came back.
I don't understand why that worked.