ive had a mandarin for about 2 years now..... if your getting one small, from my experience im afraid the only thing you could really get them to eat are pods
which you can grow yourself.... really easy to do by the way.
if your getting a larger one, you may be lucky enough (like me) that will eat other food sources.
I've pretty much got no pods
left, the mandarin destroys them in a matter of days when I add them in. all I do is just feed it brine with vitamin solution and all is well.
never really had any trouble with it at the moment