Need advice on invasive something...

[Phormium]

My 120 gal reef tank has been active and problem-free (knock on wood) for at least 5 years. I haven’t added anything new in a long time but the last fish were in 6 weeks of QT and the last corals were inspected and dipped. Ages ago, I thought I had an Aiptasia infection (as waaaay back at one point near the start I did) because I saw tiny polyps, with tiny tubes growing on the rocks. They’d retract into their tubes if you came close and they were mainly about 1/4” tall, brownish-green generally. I snapped off some of the smaller pieces of rock they grew on and took out some of the “clumps”. The clump would dry out leaving a small cluster of empty tubes. Because that didn’t seem to match Aiptasia, I scrubbed them from the rocks over and over again (and, maybe naively turned on the water polisher) and they eventually gave up and disappeared. But now they are back and more aggressive than before and have popped up all over. I need help on determining what they are and what I might need to do, if anything, about them. Any ideas?

[Dearth]

Pictures would help in positive IDs to better give you an answer

[Phormium]

Thanks, I’m going to try but they are tiny. I do have a dry clump that I can photo. I’ll see what my phone camera can pick up...

[Phormium]

Stupid phone camera. Anyway here’s one of the dry clump and one in the tank.

[shrimp]

Hydroids
Hard to get rid off. I ended up selling my live rock.

[Phormium]

Hmmm, seems like very bad news. Apart from dismantling, would anything else help? Maybe not an iron-clad solution like boiling all my rock, but how about something like smothering them in epoxy, or just keep scrubbing/tweezing every week during maintenance, reduce feeding, anything else maybe...???