If you are using a stock model tank like that then your anemone is starving. Hard to believe, since you are feeding it. But most anemone in our tanks are photosynthetic. They need intense lighting, from several t5ho bulbs, mh
, or high output LED
to provide what they need to survive. Even though you are feeding, most of the time we give anemone food that is hard for them to digest due to the size and ends up costing them more energy to digest it then they are getting from the small meal. For your anemone to survive, you will need to upgrade your lighting and do some more reading on anemone care.