I live in southwest Florida and just return to my home after Hurricane Irma. My house was built in '64 and has a porcelain coated cast iron tub. Upon opening the house after no power for 6 days, the tub is terribly stained. I have never seen anything like this before. It is not mold, you can't scratch it off with your fingernail. I cleaned the tub with a bleach solution, then Soft Scrub with Oxy. After that, it looked somewhat normal.
The next day, the tub was back to the nasty stain. Any thoughts on ways to get rid of the stain? Cleaning with a TSP solution has been suggested. Any thoughts?