Yes Ann years of scrubbing it with an abrasive will scratch the surface and make it difficult to make that pristine sheen. Sounds like you have hard water and to bad their’s not a water softer in line but that’s pricey over the years however it helps your water lines stay healthy longer as well as laundry detergent to go farther and shampoo to lather easier…vinegar is also abrasive aka caustic.
I have heard the adage if it’s yellow let it mellow and if it’s brown flush it down but the protein in urine will cause this in your bowl.
So that being said, use the oxy treatment once a week and if you get dissatisfied it might be time to save up for a new one.

This could well be a Hard Water deposit of limescale. Try a limescale descaler. I’m a Brit female 83 yrs old but also an ex drug company chemist. If you experience limescale in a kettle or elsewhere, like in a shower or even bath. I’d suggest you contact your local water company and ask them about the hardness of their water supply.
It could also be a bacterial problem – which should be sorted by bleach.
Regards Mary

Hi Ann, hmm that’s a tough one. If the pumice stone is wet it shouldn’t cause any scratches. You can also try CLR to get that dark grey line out but I’ve personally never dealt with this cleaning problem before.

Sparkle window cleaner DOES NOT STREAK.
But many paper towels do, if you press hard enough.

For hard water residue, I use CLR… works great! It’s also good for water lines in vases.

I have found that every cleaner streaks, even though they advertise that it doesn’t. It’s all in the wiping. I usually use paper towels first and follow up buffing it with a micro fiber cloth as a final step. I literally buff the mirror till the streaks disappear. The 2nd wipe must be very dry & clean.
Ariana offered an excellent suggestion… using a little bit of ammonia. but always buff it till the streaks are gone. Good luck!!!

Look up Simix… Similar to oxiclean, but proven to kill the viruses