What is this, algae, tube worms, coral???

[badwolf]

look like colonial hydroids to me. I had them didn't multiply for ages then went to t5's and they did get rid while there aren't many

 

[SushiGirl]

Colonial hydroids.

 

[LeslieH]

I'd still like to see a close up before deciding whether they're feather duster polychaetes or hydroids.

 

[socalmicskills]

Sorry, the rock is in the sump now.

 

[badwolf]

Sorry, the rock is in the sump now.

good idea you can leave the hydroids there they shouldn't spread back to display as long as there are no more in it anyway.

 

[katsuma]

https://drive.google.com/open?id=143hb_vY8IsWwWjgrUNZZPW2BebdwAO3s

I've not long got this coral, not sure what it is but I've noticed some sort of work like thing that keeps popping in and out. Don't know if it's good or bad. Any ideas?