[Delphinus]

With aiptasia, you can try that product (I've never heard of it, but hey it's worth a try, right?), or Joe's Juice, or do what I do, and use kalk.

But. !! Here's the catch, what I suggest, is go to U.F.A. and buy a syringe or two, and a nice stout needle. Use the needle to inject the aptasia (be quick - they retreat pretty past). If you're using kalk, be sure to inject the kalk goo at the bottom of the jar, and not just the kalk water itself (that's just a spicy meal). Using kalk (and particularly using the powder residue I get at the bottom when mixing up the kalk), I've had pretty decent success of permanent removal. The only exceptions being when I've basically "missed" getting the needle into the anemone. Then they come back after a week or two and I have to try again.

However ...

Hydroids... ugh, yeah, you're almost better off doing what Slick Fork has suggested and just take the rock out. Try drying the rock or try powerwashing it.

If it's just a small patch, you can try some underwater epoxy and smothering them. There's a pretty good chance they'll find a way around it though, especially if there are lots of them.

I tried CC stars to rid my rock of them, but they didn't do the trick.