in my basement we have a kohler toilet, and it came with the house, probably decades old. it never has any mineral deposit. directly above it on the main floor we have a relatively new one from a box store. it always has mineral deposits it in and we are constantly cleaning it. we do not have a water softener. at certain times of the year, both toilets see about the same use. we have high mineral content water, so its not a surprise to see minerals. is there something about the glazed surface of a kohler (or other brands?) that seems to resist mineral deposit? thanks