a refugium will only be needed if you tank cannot support a large enough pod population without. But I do agree with some of these other comments, I would make a dedicated area in the tank somewhere, usually back behind or beneath some rockwork, where you can creat a place for the pods without fear of being eaten.
If this is a new setup as mentioned before, I would give the tank a few months at least, 6 would be better. Most new tanks will see an abundance of pods for the first several months, then as they consume their food sources they'll die back. So the tank may have enough right now, but the mandarin could easily decimate them right out of the tank completely in no time. You will want to dose the tank with phytoplankton to help pod populations as well. If you have a sump, may even want to stick some rubble rock there as well, this will act as a "refugium" for the pods. Heck, even some larger pieces down there wouldn't hurt, such as a few nice big chunks of rock surrounding the return pump. Pods will breed around those rocks and their nauplii will get sucked up in that return and end up in the display to grow and feed the mandarin (pod nauplii are free swimming in the water column and far to tiny for the return pump impellar to hurt em any.)