They are very tough corals to keep. You should be feeding it every few days. A useful trick is to cut off the bottom of a 2-liter soda bottle then put the soda bottle over it and squirt food in through the top of it. This will keep other animals from stealing its food, and will give it a lot of time to catch it and eat.
Good luck -- they are one of the hardest corals to keep in this hobby.