[OCDP]

Hahaha it really is like crack for fish.

Your mandarin might not be interested in it because he can't get at it.. mandarins will eat what is underneath their face, and I am not sure if a mandarin would swim to the top of the tank to get soem cyclopeeze.

Try this.. ( i have NO idea if it will work ) i seen it on RC somewhere.
Get an empty container of jam, put pellets, frozen foods (whatever he eats...) and set it on the bottom of the tank (assuming none of your other fish are big enough to get in the jar) ... hopefully the food will stay in the jar, thast why pellets work best (try what you can it wont hurt anything)

The objective is to setup a "diner" for the Mandarin, allowing him to enter the jar and eat without having to compete for food. Just make sure your mandarin notices the jar ....

I honestly don't know if it will work..... just trying to help

Good luck

*edit* doesn't HAVE to be a jam jar... just some type of jar with a small opening , or big enough for the mandarin to get through, and to keep out any other fish (assuming your tankmates are biggers)