Well if the breeder told you to put him in a smaller tub that's ok. But to put him in with a female is a guarantee he isn't going to want to eat. He will want to breed with the female. 900grams is a great weight, just make sure to monitor any weight losses if he continues to refuse meals. Either you want to breed him or you want to get him back on food.
His breeder says he stops every year and after he's with her he usually starts eating again.