[adamanteus]

Hi Kane, it sounds as though you're doing great with the snake. If he was thin previously I think you're wise to fatten him back up again, you can always reduce his food intake once you're happy with his weight.
You could supplement his diet with a few pinkies.... if you just throw them into his water bowl with the fish, he will bump into them and likely eat them while he's chasing the minnows!