I am just wondering if water in different parts of the world have different chemical compositions as far as hardness/softness goes. Because when we lived in south Louisiana we had "soft" water from artesian wells. Delicious right from the tap. Hard to rinse soap off. But left toilet rings. None of the commercial products worked for me except early versions of a product called Ring King. But then the formula was changed and it didn't work any more. I tried denture tablets, Coke, all the commercial products, vinegar, bleach (not together) and finally the only thing that worked was a pumice. In metro Atlanta we have different water and it doesn't taste good from the tap but after 2 years toilets are still easy to clean and don't get rings. Curious for sure