I found this cleaner for $1 and read online that oven cleaner could be used on hard to remove soap scum in shower. First of all let me tell you I tried Every shower cleaner to remove Hard Water soap scum build up on shower. I tried scrubbing . All of the other cleaners I tried would just lighten it but not remove it entirely. Finally I read on line to try Oven Cleaner so I found this for $1. I sprayed it on and let it sit for 2 hours and scrubbed. Then applied it one more time and repeated and finally no Soap scum in shower. The only thing I didn't like it is the heavy fumes from using this product. I would use a respirator with product which might negate the savings.