My suggestions:
1.) Contact the seller to find out what he was eating before and use that for the next feeding. If you don't have his contact info anymore, I'd start experimenting on the type of food he would take - I suggest you try a live fuzzy rat next (or the appropriate size for your bp's size).
2.) Get a digital kitchen scale and weigh him every week to monitor his weight. Not too much of a worry if he's not losing weight.
3.) Move him to a 6 qt tub. Just because the 15 qt worked for your female doesn't mean it will work for your male. Each of them have different "personalities". The recommended enclosure size for a hatchling is the 6 qt one - it has the most success, so you might want to try that until your kiddo settles in and starts feeding for ya.
Good luck!