Munnid isopods are algae grazing micro fauna that are common in reef tanks. These graze on algae films in the tank, and become food for many species of fish. Highly recommended that if you keep mandarins, that your tank be seeding with isopods and tisbe copepods for best success. 
 
Difficult to mass produce, but we have some tanks that are fishless that we grow algae in, which these thrive.  Harvesting is not as easy, we have to capture them one at a time! 
 
Adding to your tank is easy though. Shake bottle and pour them in with the lights off. Fill bottle with tank water, and repeat once or twice to get them all into your tank.