I used to keep one, thinking I have sufficient pods in my nano tank to sustain it, till I watch it grow thinner day by day and it died eventually. It lived for 2 months, and I had a fuge in my IOS with cheato too (pod cultivation area).
So learning from experience (which isn't a good thing in this case), I wouldn't advice on keeping a mandarin unless you have a stable, continuous food source to sustain it (with the exception of pellet or mysis feeding ones), hence the reason for posting the feeding question to you.
Here's a link from Nano-reef on keeping Mandarin fishes in a nano tank.