I would suggest more than that. I would make a mixture to freeze with mysis, shrimp, mussel, krill, clam, squid, selcon, etc. really mix it up. In the wild they may very well eat a diversity of things within that size range (eg juvenile fish, eggs, plankton, etc). at least every once in awhile, I would mix it up more than brine and mysis. The phyto may even be a bit too small, but won't hurt. Big issue is water quality. It can deteriorate fast trying to keep an animal of that size long term.