I am one of the people that suggest not feeding silversides. I have been (( successfully )) keeping hosting anemones for 20+ years (( had one S. haddoni in my care for 15 years )).
Even though certain people won't believe it, I did lose an otherwise healthy H. malu to one. Know another experienced anemone keeper that had the same issue.
BTW --- an E. quadricolor does not anything close to a silverside in the wild. Something about the size of mysis is about as large as it will get. In addition, for an already stressed anemone, the smaller the piece of food the easier it will be for the anemone to digest it.
What size tank do you have?
What lights do you have?