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:

Are we sure these are colonial hydroids?

I found some of these in my tank- and I'm really not convinced that they're colonial hydroids. Every single ID thread I've come across has them labeled as colonial hydroids, but based on a few observations I've made, I'm not convinced. Here are some pics of the exact type I'm talking about...

www.reef2reef.com

Hydroid advice. - Reef Central Online Community

Hydroid advice. Reef Discussion

www.reefcentral.com

Edit: Just to add, these may not be tubes at all in a traditional sense - it may just be the hydroid's flesh.