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Calcium is dull gray, but it is shiny when scratched. Other physical properties. Calcium is an excellent conductor of electricity. It is very soft and easily scratched. Chemical properties. Calcium reacts rapidly with air to form a coating of gray oxide, and it burns with a red flame.
Maintaining Pool Calcium Hardness. To keep pool water balanced, calcium hardness Is one of the most important levels to maintain. Calcium hardness, is the measure of how hard or soft your pool water is, and measures how much calcium is dissolved in your pool water. I explain calcium hardness in more detail in our swimming pool glossary.