Are these some sort of hydroid?

[cbjay10]

They aren’t growing very rapidly, don’t have the feathery tips that I’ve seen on other hydroids but I’m not sure what else they might be. Anyone have a clue?

 

[WheatToast]

Might also be bryozoans (though I'm not too good with these and hydroids), which comprise a very diverse phylum of animals. These are harmless filter-feeders.
http://reefkeeping.com/issues/2003-10/rs/index.php
https://www.reeflex.net/kategorie/182.html

 

[cbjay10]

Possibly. Those have a more feathery appearance too though. Maybe a kind of sponge?