How can I clean calcium deposits off my mirror?

In Central Texas, we have very hard water (high calcium levels). I cope with this by using white vinegar. The 5-7% acid level will react with the calcium to make water-soluable salt which is easily removed.

Apply vinegar to a damp, clean cloth, or use a spray bottle to apply vinegar to the affected areas. Let soak for 30-45 seconds, then wipe away with a clean dry cloth.

Here is a little known secret, don't tell anyone!!!! "Bar Keepers Friend" powered cleaner works miracles with fogged, rain stained and calcium covered glass. It contains acyclic acid and a mirco fine abrasive. It cleans glass, head light lenses and fiberglass like crazy and give you a very smooth polished finish. you can also use it with a buffing wheel or by hand. You can find this product at most any grocery store.

Put full strength vinegar in a spray bottle. If you can lay the mirror flat, this will work the best, otherwise make sure you keep the mirror wet. Never do this with a dry mirror. Take a BRAND NEW single edge razor blade and angle it downward 50-80 degrees or so. Never try a used blade as any imperfections on the blade could/will scratch the mirror. Using a small amount of downward pressure, start sliding the blade back and forth across the glass. You'll feel or hear it cutting off the buildup. When the blades feels smooth on the glass then move along to the next spot. KEEP the mirror WET! If you don't trust yourself holding the bare blade in your hand, just get a slide-in type blade holder. This worked far better for me than any of the commercial sprays I tried. This also works fantastic on ranges with glass tops. In fact, Samsung recommends this method over any & all abrasives.