How do I get tough calcium off my sliding glass door?

Fill a spray bottle with a 50/50 solution of Dawn dish soap and vinegar. Spray it on the calcium stains and let it work. If they are tougher stains, you may have to scrub with a plastic scrubbie!

Lime away

You can use magic eraser for tough stains on glass doors. Many times, calcium deposits etch glass overtime which means it won't clean off since this damages the glass.

If you’re judicious with a single edge razor blade, it can be used at a shallow angle on the glass.

CLR.

Here's a video that might help - https://www.youtube.com/watch?v=HhatW60iqMM