Enter the Manly Housekeeper. He explains why soap scum and hard water become such a problem and then tests 6 well known products to see which works best. He taped off 6 sections of a glass shower wall and took pictures of how each one worked. Check out the whole article at:
http://www.themanlyhousekeeper.com/2011/03/11/solved-soap-scum-and-hard-water-stains/
Needless to say I promptly went out and got Barkeeper’s Friend to clean my showers. Thank you to the Manly Housekeeper for the work and great information! I’ll be checking out more of your articles.