Odd fan like worm

[A13xander60]

I'm trying to get my tank back in order after a bit of neglect after ich got into my tank and wiped it out.

I've got the emerald crabs in to clean up the bubble algae, but I have loads of these odd fan worms in the tank and in the AIO sump areas at the back (Chambers 1 & 2), just wondered what they are, if they are harmful to corals and fish and if I need to remove them.

Thanks :)

 

[Osprey223]

They look like small feather duster worms. Those kinds can reproduce and spread a lot but I always love them in my tanks. Extra filter feeder for you!