How do you clean a black tub?

You can try to use some vinegar to clean away the old soap scum. More than likely that is the issue that is causing the tub to look so badly. Just mix some cleaning vinegar into some hot water and wipe away.

Give Bar Keeper's Friend a try, Esther. it's commonly available at the store near the other cleansers (like Ajax or Comet).

Hi Esther! Everywhere I researched, distilled white vinegar on a soft sponge was recommended for black tubs (and tiles). Avoid abrasive cleaners that will damage and dull the finish.

Hi Esther. I'm Cindy. I recommend that you use a product called CLR. You spray it on and WALK AWAY. Let it do "it's thing" for 15 or 20 minutes. Then come back and wipe it all up with a clean soft cloth. It may cost a little more than the average bathroom cleaner, but it is so worth it. Good luck Esther.

And if CLR doesn't work, try Lime Away. Worked in my toilet bowl when nothing else did. Water often has different kinds of scale. Sometimes you need to try different chemicals to find one that works. In my part of the country, we have gypsum in our water. Vinegar was a joke. Keep trying... you'll find something!

Part 2 - Haha! I struggle with nasty water stains constantly. My sunroom windows were nearly opaque from lawn sprinkler misting them when I moved into this house 10 years ago. I used Turtle Wax Rubbing Compound and it literally made my windows sparkle with minimal effort. Works on porcelain and acrylic with excellent results.