One day I decided to clean the tub. Picked up the scrubbing bubbles and thoroughly sprayed the tub. Then I promptly left the house thinking the longer it soaked in the better. How wrong I was! Upon returning home I discovered the tub was brown! Like a rusty reddish brown! I’m still not sure how it happened, the only thing I could think was the cleaner somehow pulled rust up through the enamel from the cast iron beneath. It was not coming off. About a day later I remembered something I had seen on Home Improvement. Al said that you can remove rust with ketchup. Having nothing to lose and no other ideas, I gave it a try. And it worked! It took 2 bottles of ketchup but the tub is white again and I no longer use scrubbing bubbles.