There's also those marine grass shrimp. They won't croak in the saltwater like the ghost shrimp, so if he's shy about chasing the food while you watch they'll last a little longer.

How long ago did you move him to the different tank? If there was something bullying him in the previous tank, and then he went through a traumatic netting experience, he may not eat right away. If it's been awhile even in the 40b, then there might be something else causing his problem.

The frozen food... when you thaw it, do you drain it? If it seems like the run off is chunky, or slimy, the food may be bad. Every time food is defrosted and refrozen it loses some of its nutrition. And mysis in particular gets really nasty. I make my own food mix, so I know my food has already been partially defrosted once, so if I defrost more than I need, I never refreeze it for later use. And you never know how many times the temperature drops in the freezer at the LFS as people browse.