In my experience, keeping even a single mandarin (or other dragonets) in even a large tank is a difficult proposition and not to be taken lightly. Unless you can be certain that the fish will accept non-live foods, a single mandarin will decimate even a tank that seems abundantly overpopulated with copepods and amphipods. It takes a lot of attention and dedication to keep these little guys alive and healthy.
Many years ago, I was checking my 75g at night when it appeared that the sand bed was moving around. A quick inspection with a flashlight revealed gazillions of amphipods. Literally 8-10 per square inch of sand. Copepods were all over the glass. Some people would probably have called this plague proportions. I thought "great, I'll pick up a dragonet sometime"... thinking there would be absolutely no problem keeping one alive in that environment. I found a nice little red scooter blenny (N. ocellatus) at my LFS. He would even accept some frozen foods. I thought, no problem. 4 months later, there was not a pod of any kind to be seen in that tank, and the only difference had been the addition of that dragonet. He fed 24 hours a day. I managed to keep him alive for a little more than 2 years, after which he simply disappeared. I can't say he starved, but I can't say he didn't, either. He did not escape the tank. But in any case, it was a real challenge keeping him well-fed, and I have serious doubts that I succeeded.
I would just assume that culturing or purchasing pods is going to be necessary... and purchasing enough of them to keep just one fish alive (without culturing) could break a lot of banks.
