Water Filter—Is Calcite Safe?

Still trying to educate myself on a water filter for my family! One of the contaminants in my water are nitrates. I just discovered this as I was looking through my city water report. In an instant, I switched from being a carbon block advocate, to loving the idea of reverse osmosis (I have always written reverse osmosis off, after reading that it removes essential minerals from the water, and leaves it with a low ph.