The mysis and formula 1 FLAKE are very good Ocean Nutrition also makes a flake food known as Prime Reef which would be good. I think if they are that small the frozen formula 1 might be difficult for them to eat becuase of the gelatine.
I also feed mine a blended seafood mix. You can run it in the blender until you get the size pieces you need/want.
Just add some nori, shrimp, scallops, clams, squid, fish, roe, cyclop-eze, selcon etc. and just enough saltwater to keep the blender from siezing. Take the resulting goop and freeze in thin sheets inside plastic sandwich bags. Break off a bit and thaw it in tank water before feeding.