If you have the right setup/mature tank/mature refugium, they're not that difficult to keep.
From ORA's website:
"All of ORA’s captive bred mandarins will accept a variety of prepared frozen and dry foods upon acclimation to their new tank. They may be offered Nutramar Ova, finely chopped Hikari Frozen Blood Worms, fish roe, frozen or live baby brine shrimp, frozen daphnia, and New Life SPECTRUM Small Fish Formula pellets. Some have also shown interest in Cyclopeeze."