This always works for me! How to easy clean your nasty toilet ring

Try a product called Iron Out. You can use it for a lot of different types of stains that build up in toilets, dishwashers, washing machines, etc. You can get it at any hardware store. I'm in PA, though, so I don't know if it's available in all states. This worked for me, but the minerals in your water may be different than mine and it may not work the same for you. Good luck!