100 feather dusters

I have a rock in my tank and the side is coverddddd in them. Just sharing the picture lol

 

I've just noticed 3 or 4 popping up around my tank, how do they multiply? and they're good right?

 

They do multiply, not certain on how fast, but they are good

 

That variety o feather duster usually lives in the exit chamber of my protein skimmer. They're a good thing but like anything too much of a good thing is a problem if tey take over.

 

I have a few white, swirl tubes on my glass with dusters kind of strange but cool

 

I have 200 or so in my 90. I always heard if you have to many some will just die off.