Any product that you don't wipe off will result in build up over time. Proper shower maintenance, and especially for natural stone, is very good ventilation (use fan and run for 15 minutes after shower), squeegee the walls after each use and wipe with a microfiber towel. It doesn't take that long (minutes). It's a habit you develop that will extend the life of your shower and minimize more serious "maintenance issues". Most just do it while still inside the shower. Now, once a week use a PH neutral cleaner specified for marble/natural stone. Spray and wipe with microfiber cloth. Our clients like MB Stone Care MB-5.