I have tried mandarins in both applications, fish only and reef. The only thing to really concern yourself with is how many you will have at one time. Two male mandarins will fight, like beta's, until one dead. If I remember correctly, the long antennae, on the dorsal fin, indicates female and the short antennae would be a male. I've had two in a tank at one time and only one would survive, needless to say, that I learned the hard way about them myself. Remember, two males will fight, but two females will be alright....