Damn, how did I miss this thread.
I keep a mandarin in a ten. Like aresgod said, I lost one already. If you're curious about my project, check out my thread in the saltwater main section OCC mentioned earlier.
A healthy mandarin can wipe out a pod population in a ten gallon in no time. With my new specimen, this happened in a matter of 3-4 days. Simply amazing... I've actually posted some pics on various threads with the pods in view on the glass. Now they are nearly all gone. The amphipods come out at night, so the tank isn't totally barren, and there are some in the pod pile, continuing to reproduce and infest the scrubber pads I have in there (for more surface area, imprisoned by rocks to keep the fish out), but the ones visible in the tank are pretty much history.
Obviously, I haven't abandoned my experiment, and I still honestly believe it is possible to keep a healthy and thriving mandarin in a nano environment. To this extent, I'm willing to buy aquacultured copepods (see seapods.com for a list of online retailers) and inject them into the tank as needed. I tried culturing them on my own, following the detailed advice of another pod company, but I feel this did not work.
I have some speculations on my new mandarin eating food other than pods, but I'd rather not make any assumptions as I don't really have any facts right now.
Check out my thread and do some online research on mandarins if you're interested in keeping them. They require specialized care, but they can be kept in nano tanks if one makes sure the fish is getting enough food.