The trick with Mandarins is to watch the few in the store eat something frozen(or better yet pellet) and not spit it out
. If it will eat for them then it will eat for you. Especially since your tank will be better taken care of. Right?
On the same hand, feeding a mandarin pods or BS will give them the all important nutri's they really like for growth to be best as possible. Live brine shrimp can be bought from most LFS, and fed accordingly.
I've even seen a Mandarin fed baby guppies and mollies that stay alive in the SW.