well, part of the problem...
TUBE anemones are filter feeders-mysis shrimp or smaller. Feeding them bigger pieces is not healthy or helpfull, and if they are actually taking that in, it means they are starving. They are also non-photosynthetic, so you need to feed them at least 3x a week.
I had one, a few years ago, and I want another. REALLY neat critters, so pretty. I'd move it under a ledge and start direct feeding it mysis from a turkey baster, like 4 pieces 3-4 times a week until its healthy, then 2-3 times a week thereafter. MAYBE more, since it IS a filter feeder.
and no, they don't eat fish. Unless they are EXTREMELY starving, and even then they don't have the parts to digest it.