Lots of mini Feather dusters?

[kesuk]

I noticed one of these a few months ago attached to one of my coral frags, now they seem to be spreading everywhere. They don’t appear to be bothering anything much but they are crowding out a Zoa frag. One of the worms was moving in the second photos. Any idea what they are and if they are a concern?

 

[NashobaTek]

Looks like feather duster to me.

 

[reefwiser]

They are a great addition to a tank. If they continue to grow. This means you have a lot of micro life in your aquarium. I have had a whole sump covered with them.

 

[kesuk]

thanks, glad to hear they aren't a concern

 

[1ByLand2BySea]

They are good filter feeders and nothing bad at all.