I've have kept quite a few mandarins... I haven't much luck with the splendidus ones. They are quite finicky although the closest I got to feeding one was hatching baby brine shrimps. It would swim up the sides of the tank and siphon them one by one.
If you gotta try mandarins, try the psychedelic kinds. They're less finicky from my experience, and the guy from King Ed's agrees. I bought one abt 8 months back...and he's still fat and happy. He was initially a little shy, but try warming him up with bloodworms. Then gradually, try brineshrimp. Now I have him on mysis. You gotta have the patience to try to place food in its path...and once you have gotten him used to a feeding space, when he sees ya in front of the tank, he will go check out the spot for food. I have my mandarin feeding off some flatter live rock near the top of my tank. Helps that my other fish are quite passive.
