They do need to be spot fed a few times a week. I use finely chopped up krill, I have a stick that I use to feed it with and I place a small piece in the center, it grabs the stick before I can get it into the center and pulls this krill right in.
I don't think they need to much all at once, just a small piece will be fine. I have not even had mine for a week yet and already I have noticed it extending and looking fuller. I know the store where I got it did not feed it anything except for what fell in the water and the fish did not catch.
I also add some Kent micro-vert twice a week for my feather dusters as well. I am using this stuff very very cautiously to not pollute my tank. Time will tell if it helps them out too. But I think the tube anemone can eat some of this stuff and the fine stuff the dusters eat too. I just would not rely on this stuff alone.
So feed it a couple times a week with some frozen foods in small amounts.
Debbie