You can buy copepods and add them to your tank. Put them in the tank at night when the lights are off and the fish are asleep so they will have a better chance of making it to safety and multiplying. You can also put a very porous piece of live rock in your refugium and pour some of them in with it. They will multiply. After a few weeks, exchange that rock out with a rock from your display tank. Keep alternating and you should have a good colony of them shortly. Mine would only eat copepods. He didn't make it too long...not because there was nothing to eat, but because something bit a small hole in his side and he died a few days later. They are very slow movers and if you have ANY predators, you may not want to get one.