I have these things all over my tank. They like to grab onto frag plugs or rocks but I also see then free floating. Crown looks like tiny white clove polyps but these are not cloves for sure. I don't this these are Hydroids either. Here are some pics. Size is about 1-2cm long.
They're micro feather dusters as mentioned. They don't necessarily "free float" but they're worms. They'll go where they want and build a little tube for their house there.
Thanks everyone. Any idea what eats them? I have a Six Line and Melanurus and they don't eat these things. I just have so many and they are growing in between Zoa colonies. Zoa retract from them so I am assuming these are harmful to corals.
Both should eat them. However, if you have had a recent explosion in quantities, give it some time and they'll decrease in population. They're beneficial filter feeders and will likely make their way to your sump or back into the shadows eventually and you won't see as many of them but decreasing nutrients helps control their numbers as well.