The water at my house is somewhat hard, but not as hard as the well water you have I'm sure.
Not sure this is a magic bullet, but when I looked into this I was told to get something called "The Works" at Wal-Mart that does seem to help. I also read if it's real bad to try using pumice, not sure how to spell that.
I also used a blue scrubbing pad I got at Wal-Mart that says it will not scratch surfaces along with soft scrub cleanser, and that removed all the stains.
Not sure if any of that is 100% surface safe.
I wonder if toilet manufacturers will provide info. on how to safely clean their toilets and what products to use?