You could bump him to a 5 day feeding schedule instead of uping the prey amount. Also, getting a scale will give you a more accurate reading on what he is gaining or not gaining. I know my pastel male went through a phase of looking thin, even though he was clean and eating a rat pup every week. If I didnt have a scale to tell me he was gaining 100 grams a month, I would have been freakin out.