I've had these in my tank a while, there's a ton of them. They've got sweepers that come out like a feather duster.
They will decrease in numbers as your tank matures, especially if you keep your nutrients under control. They seem to like places out of the light like in the over flow, under ledges, etc. At least that's what I've read. I have them in my nano and even a few in my DT.
