pH is the measure of acidity or alkalinity.  The pH Scale runs from 1 to 14.  A reading below 7 is acidic and above 7 is basic or alkaline.  We want to keep our pool water slightly on the alkaline side of the scale between 7.2 & 7.6.  The pH in a concrete pool will tend to drift upward because of the high alkaline content of the cement plaster.  Small amounts of muriatic acid will need to added to the pool to lower the pH to the 7.4 - 7.6 range.

Total alkalinity helps buffer pH in a well-maintained pool.  A range or 80 - 120 PPM is ideal.   The total alkalinity will tend to drift lower during the swimming season and can be increased with the addition of baking soda.

Calcium hardness helps protect your plaster pool surface and pool equipment.  A calcium hardness of 250 - 400 PPM is the ideal range to maintain.  A low calcium hardness level combined with aggressive water (pH below 7.2) will result in the etching deterioration of the marcite plaster.  This condition is irreversible and can only be corrected by resurfacing.  A high level combined with scaling water (pH above 7.8) will cause staining and calcium scale deposits.

TIP: Most pools in our area require a weekly pH adjustment (usually a pint or a quart) of muriatic acid, a monthly Total Alkalinity adjustment (usually a pound or two of baking soda) and no adjustment in the Calcium Hardness level (thanks to our hard water).