Calcium Hardness-Where does it come from?

[frankmcs]

My pool calcium hardness is at 650, the top level recommended. My pool “fill water” calcium hardness tested at 100. How is my pool water climbing to 650?

 

[mknauss]

Evaporation.
The calcium stays in the pool water. You add more water (every day in summer) with calcium. It builds.
You have very low CH fill water for your area. I suspect you are mixing in some non - Colorado River water. The CH will likely climb in your fill water as you approach summer.

 

[Rancho Cost-a-Lotta]

A solar cover will slow down evaporation to help keep you from adding additional calcium. A water softener will remove the calcium before it goes into the pool. Also avoid chlorinating solids containing calcium (cal-hypo or calcium hypochlorite).