look what i found : " Mandarins tend to be rather picky eaters, preferring to feed from the bottom. Due to the relatively small size of their mouth they must be fed only small food items or finely chopped foods. As mentioned above they appear to do much better in aquariums with abundant live rock and/or plants. This may be due to the fact that there is an abundance of natural food items for them to feed on. In such an aquarium they will spend most of the day grazing amongst the substrate searching for food items such as small crustaceans (e.g. Mysids, amphipods, isopods and benthic copepods), small worms and protozoans"