I would not feed a copperband only mysis. It is a lot of shell. I feed Frozen LRS Fish Frenzy, live worms, and fresh clam (the kind you buy for people to eat that are alive at the market). I know I told someone here to switch foods because theirs was getting skinny on only mysis. The food swap fixed their problem.
Plus copperbands are pigs... I swear mine could eat 100 live black worms in one go if I let it.
The white worms are better then black. They live awhile in saltwater and keep wiggling which fish like