I've had one in my Rimless that only eats pods for almost a year now, never gotten her to eat prep foods. When I first got her she had a pinched belly but now she's fat and happy. I built my whole system around the fact that I wanted to keep one, so I did my homework and found that the best way to keep a healthy mandarin long term is to have a fuge with Chaeto. I have a fairly large 15 gallon fuge (my whole system is about 70 gal; almost 25% of it is Fuge! ) with 2 big ol' balls of Chaeto; the thing is a pod factory. Then every 8 months or so I replenish the Pod population by adding AlgaGen ReefPods Tisbe Live Aquacultured Copepods to the fuge.

I read the main problem with this fish they eat so many pods that if you add the pods directly to your main tank there isn't a safe place for them to repopulate (fuge) their numbers will dwindle and they will eventually all be eaten. And according to others mandarins can "eat a whole bottle of pods in a day or two",making the cost for buying pods through the roof as Demon pointed out.

Don't you have a hob fuge Miz? I thought I saw in your tank thread you did, you could try adding pods to that and see if it can keep the count up. And if not you could always add a separate "pod fuge", this Hob fuge isn't too pricey, just need a cheap light, an air pump, some more LR and Chaeto. This may seem like over kill, but i think that it's your best bet for healthy long term success.