well if he was 400 when he got picky and has put on another 100g then I'd say he's just being a ball python. They eat when they want to eat. Unless he's getting really thin I wouldn't worry about it. If you want a snake that will eat every 4 days year round, buy some colubrids.
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Josh & Krysty Hutto
J&K Reptiles
Various Ball Pythons:::
1.0 striped vanilla
1.2 Citrus Ghost and hets
1.2 Albino and hets
2.3 het Pied
1.1 Pastel (male has additional gene going on with him)
a bunch of female holdbacks and several rescue normal males
0.1 columbian boa, she's a feeding monster, controls my
over production of rats, lol
0.1 brazilian rainbow boa, another rat eating monster
1.1 corns
a BAD dog is MADE not bred, support the American Pit Bull Terrier as the greatest breed of dogs on Earth!!!!!