when should i be worried??

My enchi has not eaten in about 4-5 weeks. on 12/15/13 he weighed 284g and today he weighs 260g. i have been offering him rats every week but nothing. i have been having to treat him for mites the past 2 weeks tho. im thinking i will try a fuzzy/pup in a couple of days, but when should i start to get really worried about him. he doesn't look dehydrated and is active at night. temps and humidity are good, i did move him from his larger enclosure to a smaller one last week.

5 weeks is nothing for a ball python. Get your mite problem under control and let him settle in his new enclosure, then try it again.

he might not be eating because of the mites ... but at 280 grams he shouldn't be fasting he should still be eating with no issues .. if he is real active at night try to feed him then