I keep a pair of them. After I bought them I put them in a big fish breeder in the tank. Fed them with live pods and started adding frozen bit by bit while reducing the live food. After about a month they were greedily accepting fozen pods. Only then I released them into the tank. They feed well at feeding time, are fat and happy, mate and spawn regularly.
The key to keeping them is to find a HEALTHY pair. I was lucky, but also know of many cases where people lost their mandarins after a short while