What are these things?

[krfish]

I've got these little white things that are growing in my tank. Most of them are in my refugium. See the attached image...

 

[stanlalee]

Spirorbid worms. harmless filter feeders but you can scrape them off with a blade scrapper if you dont like them.

 

[reefboy1994]

i have those ... EVERYWHERE!

 

[mudplayerx]

Stanlalee is correct. Don't let these overgrow your pumps or pipes though as they greatly decrease water flow and can eventually damage equipment. Regular monthly maintainance of your equipment will suffice.