You mean mandarins? These fish eat specifically copepods, tiny organism the size of a period. Dragonets(species) can eat 2,000-4,000 a day. They constantly feed searching for food on live rock. This means you need a huge population of them which takes a while, plus sometimes the mandarin will demolish the population before it can multiply and the mandarin will starve. It's best to buy one already trained to eat frozen food or you can take a risk and add it to a tank w/ a large population of pods
and train it to eat frozen foods.