Help ID white stringy things on liverock?

[cheucklate]

They started off at the base of a hammer frag and have started to overtake one of my rocks. What is it, will it keep growing like this? thanks in advance

 

[TimeConsumer]

Looks like some micro calciferous feather dusters. Common, harmless, I had thousands in my sump.

 

[gone fishin]

Looks like feather dusters to me as well. In my tank they come and go.

 

[cheucklate]

tyvm