My bathtub has never been whiter!! Works great on glass shower doors too- no more soap residue! Martha Stewart's Tub Scrub - works better than any other cleaning product to get off hard water and soap residue. Here's a nontoxic but effective way to clean your tub: Add one teaspoon of liquid soap and several drops of an antibacterial essential oil (such as tea tree, eucalyptus, rosemary, or peppermint) to one cup of baking soda. Add just enough water to form a paste, and use it with a sponge or brush to scour bathtub surfaces.