We all know sometimes it's the "crazy" things that really work. Drop magnets (housed in clear plastic) into the tank of your toilet and walk away. The long-lasting magnets prevent natural minerals that exist in all water from staining your toilet bowl and building up on any metal parts of the toilet. Lime and minerals flush right down the drain.
Helpful Hint: If you have very hard water, you can remove the magnets, rinse and wipe them with a paper towel. Then reinsert them into the tank. They can also be used in humidifiers.