What does GPG or grains per gallon mean?
Parts per million or grains per gallon are both used to describe the dissolved hardness minerals contained in a water.

One part per million (PPM) is one unit of a substance out of one million units of water. Grains, or grains per gallon (GPG), is a unit of weight. It is 1/7000 of a pound. One GPG, (1gpg) is equal to 17.1 PPM.

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1. What are the minerals that cause hardness?
2. What does GPG or grains per gallon mean?
3. What is hard water?
4. What problems does hard water cause?