I was able to get mine to eat (anything now!) by mixing some live brineshrimp in with the frozen when I fed him. If he is in a tank with other fish he may not get a chance to eat though. These fish are really slow stalkers and prefer to stalk pods, etc as Charlie has already told you. My advice would be to try and isolate him until you know he is eating, then reintroduce in to the display tank or chances are he will not survive if there is not enough pods in the tank to support him.