Hydroids or something else?

[kennyry83]

I think these may be hydroids? If so should I get rid of them? They seem to have started spreading rather quickly. Recently recovered from dinos, got nutrients up from 0 and ran a UV for a couple weeks and beat it but now these dudes started popping up. (Nitrates 6.5 Phosphate .13 for reference.)

 

[Crabs McJones]

Do they have a solid stem or do they retract back into the rock? Either colonial hydroids or aiptasia

 

[kennyry83]

It looks like they have a stem, put some Joes juice on several of them.

 

[ISpeakForTheSeas]

Either Nausithoe jellyfish or hydroids:

Either colonial hydroids, or Nausithoe sp. jellyfish polyps; to my knowledge, they're not invasive (or at least not always), but they reportedly do have a nasty sting for some people:

Or jellyfish polyps, yeah - the clearest examples I know at the moment:
https://www.reef2reef.com/threads/are-we-sure-these-are-colonial-hydroids.797406/http://www.reefcentral.com/forums/showthread.php?t=2494739Edit: Just to add, these may not be tubes at all in a traditional sense - it may just be the hydroid's flesh.