Easiest way to confirm water/anti-freeze concentration would be to go to local auto-parts store and pick up a tester. The tester measures the specific gravity of the mix and tells you freeze point and boiling point (they work hand in hand).
If your "coolant" actually froze then your mix is not strong enough. I normally run water-wetter in the summer months, then flush and replace with 50/50 mix in the fall-spring months...
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