I change substrate once a week and the first 5-6 days all I smell is pine. On the last day or two I can pick up a slight scent of ammonia but only when I'm nearby. The key to raising rodents without offensive odors is to not overcrowd(with no more than 1 male per tub), deeper substrate, frequent bedding changes. It costs a bit more than skimping on bedding and overcrowding but I'll take that tradeoff any day. I also feed off males first so by the time my rodents are weaned I'm down to mostly females.