I’ve tried scrubbing it several times with bar keepers friend soft cleanser and although it improves, it never goes away completely and it always comes back.
1 point
Mr. Clean magic eraser
1 point
Paste of Comet and peroxide
1 point
2 points
Bar Keeper’s friend will get that out, I use it when things get especially grimy. I’ve used it on a similar tub before that was pretty gnarly with discoloration worse than that.
It is very abrasive though, be careful not to scrub so hard you damage it.
11 points
I don’t know how to fix your problem, but please post this image to one of the UFO communities.
3 points
10 points
Important question: What is your tub made out of?
Some cleaners may destroy it if you use them.