If you get a well fed Mandarin and if you have a good pod population in your smaller tank you will delay it's starvation, not prevent it. There is anecdotal evidence that some mandarins will eat other stuff, but it's incredibly rare.
I went to the fish store and the owner wont let me return the Mandarin but he did tell me he was feeding the him shrimp and worms for about two weeks. I took some home and have been feedin him that. He id doing great.
:cheer: