Mandarins definitely require an established tank with a healthy pod population. One thing you can do, if you have a good amount of LR in your tank, go to your LFS and ask to get or buy some "sludge" from their LR container. This stuff is the debris that falls off of LR and is usually infested with pods. I grabbed about 2 gallons of this stuff and put it behind my LR formation and within a week I saw pods all over the place and then I introduced a Mandarin and he is fine with plenty to eat. If you do, also bear in mind that if you have other fish that will eat pods, they may deplete your food supply. The sludge I used was to seed a polulation in my tank and boost the availability of food for a Mandarin.
Just a thought!!!