My petstore told me the same thing, was feeding too little for quite a while, and now I'm in the process of trying to fatten him up to where he should be cause he's underweight. Until they hit around 500 grams its good to feed them twice a week, or at least every 5 days. My guy is now on two rat pups a week, seperate feedings of course, when just a few weeks ago he was only on one small adult mouse a week.