mandarins are cool, and as mentioned, should not be added unless you have a good supply of food for them, often they will not take to feeding, only hunting
they require75 to 100 lbs of LR and a good amphipo and copepod poulation, and should not be added for at least 1yr after establihing your dets, for they will depleat your supply if you add them before it is well establihed
HTH
good luck