Back when I used aspen I spot cleaned as needed, and completely changed the substrate once a month... I'm not sure why people are saying once a week, the cost and time for that is crazy especially if you have more than one snake.
This.
I only used aspen for a short period of time, and only when I had one snake. When I made the move to an RBI rack system I dropped the aspen in favor of paper.
Thomas "Slim" Whitman
Never Met A Ball Python I Didn't Like