CALCIUM HARDNESS:

Perfect Range 200 - 400 PPM

Temperature + Total Alkalinity + pH + Calcium Hardness + Stabilizer Adjustment + TDS = Saturation Index

Calcium salts in water are hard to make suds or soap bubbles, so the water is referred to as "hard" water.  The higher the concentration of calcium in water, the harder the water is.  Water with a low concentration of Calcium is referred to as "soft" water.  Calcium is the most abundant mineral in pool water.  If calcium is too high, scale forms on pool surfaces and equipment.  If calcium is too low the water is corrosive to equipment and surfaces.  The trick is to have just the right amount of calcium to prevent corrosion and scaling.  Since other factors such as PH, temperature and total alkalinity affect how calcium is kept in solution, you must know the saturation index of the water to determine what the calcium should be.  If the total saturation index is low, calcium is needed.  If the total saturation index is high, too much calcium is present.  Since calcium can not be removed from the water, it is pretty much fixed.  For this reason, the saturation index is adjusted using other factors such as total alkalinity or PH first.  Once a minimum level of calcium is established, the saturation index is adjusted with total alkalinity and PH if possible.  Since seasonal temperature fluctuations affect the saturation index, it makes the most sense to adjust the total alkalinity because it can be increased and lowered at will.  Once calcium is too high the only way to remove it is to drain part of the pool and replace it with fresh water of low calcium.  

In extreme cases where drinking water is very high in calcium, it may be necessary to fill the pool with water that has been treated with a water softener.

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