Ok, what is the temperature of the actual basking spot? If the basking spot temps aren't high enough, he may not be digesting his food properly. Do you have a bright white light in the tank during the day? The lighter the tank (during the day) the better. A tube light and heat emitter doesn't produce much light. Won't seem like daylight.
If temps are the same for both dragons, babies like basking temps around 105-110f/40.5c-43c