I recently read some great articles on feeding Mandarins. See if you can get a copy of the Tropical Fish Hobbyist's February 2007 magazine. There are two articles about mandarins including how to keep them healthy, fed and what to look for even in a nano tank. Just in case you can't obtain a copy; here are a couple of the tips I plan on using the next time I find a mandarin.
Create a pod-pile. Sandwich and "glue" LR
rubble around some filter material (like scrubbing pads) to create a in-tank refugium. The rocks will keep most hunters away from the "mother-load" of yummies and the gaps will allow adult pods
to escape in a myriad of directions so the hunters don't just watch one area. I have a in-tank hatchery which is nice, but the fish hang around the "exit" areas for easy snacks.
Create a banquet line of pod culture jars to help supplement the tank's population. Especially in a nano, a mandarin can decimate the native population very quickly.
Buy sushi. No, really! Capelin roe purchased at an Asian grocery will be enjoyed. This is the orange fish eggs used for sushi. The only problem is how to feed the mandarin and not the rest of the tank. I used a turkey baster but my last mandarin did not like approaching on anything but his terms. One of the authors had another idea with a very narrow glass jar (like a jelly or olive jar just big enough for a mandarin to enter) with plexiglass bent around the jar and coming up out of the water to act as a handle. As long as the roe is placed in the back of the jar, and slowly lowered in, the roe stays put. I was planning on further creating a special feeding zone for the jar so the larger fish couldn't harass the mandarin as much during feeding.
From personal experience it is heartbreaking to fall in love with the face of a mandarin and then see it slowly starve to death. Fish4brains - even though you have a larger tank, a couple of these ideas might be a good idea to have ready "just in case".