Hello K Sci,
This is a bit of an aside, but you might find it helpful. Calcium deposits on plumbing (and everything else) can be softened up with acids. I started with vinegar, proceeded to CLR, and now use a bowl cleaner with hydrochloric acid. Wear gloves, use eye protection, and be sure to clean it out before using the toilet! Product is called "Acidic Toilet Bowl Cleaner" Zep brand, found it at Home Depot. It helps a lot, greatly decreases the scrubbing.
Incidentally, it also works great for removing calcium deposits from ceramic pots.
Approximate chemistry is this:
Calcium "Lime" rings are mainly Calcium Carbonate, CaCO3. Hydrochloric acid is HCl. Mix them and you end up with Carbon Dioxide--CO2 (you'll see the bubbles and foam), water--H2O, and Calcium Chloride--CaCl2. Calcium chloride is way more water soluble than calcium carbonate. It dissolves in water and washes away.
Anyhow, that's how it works in Arizona, your results may vary! I had to look up the chemistry, any real chemists out there, please feel free to correct me!
Even further afield, here's some interesting information about using old lime deposits in old pipes as construction material. (Scroll down to the section on "The Aqueduct as a Stone Quarry".)
Eifel Aqueduct - Wikipedia
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