Personally I'd offer once a week, not once a month. I think even with adults most people average about 10 days between feedings. You may be up against the 1000 gram wall, seems like all my ball pythons hit that size around 950 grams or so and stop eating for weeks or months at a time. Not to worry, they will start up again. You may also want to try to offer a fresh killed mouse instead of a rat, or even an ASF. Seems to get my picky snakes eating again when I change things up. Also, you should really get a scale to make sure the rodents are no bigger than 10% of the snakes body weight. I fed some over sized rodents before I had my scale and the snakes ate them but went off of food right after that. Now I'll never go above 10% and my snakes are regular eaters again.