CALCIUM HARDNESS
Calcium hardness is the measure of dissolved calcium minerals in pool water.

Pool water that has a low level of calcium hardness (expressed as ppm of calcium carbonate) will tend to be aggressive, leading to equipment corrosion and etching in plaster and masonry pools.

Pools with high levels of calcium hardness typically have cloudy water and scale (mineral deposits) forming on pool surfaces and related equipment. High calcium hardness in pools is usually found where natural fill water has high calcium levels and in pool systems where calcium containing chlorine is used.

Typically, the desired range of hardness is 200-400 ppm.

HOW POOL pH AND ALKALINITY ARE RELATED
Research studies have shown that there is clearly a relationship between pool pH and the total alkalinity present. In general, when alkalinity increases, the pH of the pool tends to be higher. More specifically, when alkalinity is adjusted to the range of 80 to 150 ppm it maximizes the likelihood that the pool pH will hold in the range of 7.2 to 7.8.

A second important conclusion that can be drawn from our research is that when the pool pH is low, i.e., less than 7.2, the total alkalinity is also low, filely always below 70ppm. Consequently, when the pool pH is low there will always be a need to raise the total alkalinity.

AVAILABLE CHLORINE
The National Spa and Pool institute recommends maintaining the available chlorine level between 1.0 and 3.0 ppm. If too little chlorine is present, less than 0.6 ppm for example, there may not be enough disinfecting power to kill pathogens, resulting in the build-up of unpleasant odors and eye-irritating chloramines in the water. If too much chlorine is added, it wastes money.

Most suppliers also recommend periodic super-chlorination to prevent build-up of specific pool impurities. Bathers should not be in the pool during the super-chlorination process.

pH
pH is the measure of relative acidity and basicity on a scale of 1 to 14. The preferred pH for pool water is specified by the National Spa & Pool Institute (NSPI) as 7.2 to 7.8, with 7.4 to 7.6 considered ideal.

When pH is too low, staining and corrosion of pool surfaces and metal fittings can occur. When the pH is too high, scaling and cloudy water can result. Chlorine inefficiency and eye irritation can occur when the pH deviates from either end of the recommended range -- either too high or too low.

Maintaining pool pH at the high end of the acceptable range will help reduce the formation of eye and skin-irritating chloramines. Chloramines also tie up chlorine and reduce its effectiveness in killing bacteria and algae. Bathers introduce ammonia and amines into the pool through their perspiration and other body fluids. The chemical reaction of ammonia and amines with chlorine creates mono-, di-, and trichloramines. Although the chemistry is fairly complex, the tendency for chloramines to form and persist in pool water is significantly reduced when pH is maintained at the high end of the acceptable range.

TOTAL ALKALINITY
Total Alkalinity is essentially a measure of dissolved bicarbonates in the water. It is also a measure of the ability of the water to resist changes in pH when acids (low pH) or bases (high pH) are added to the water.

The total alkalinity of a swimming pool should be kept sufficiently high to stabilize pH, optimize sanitizer efficiency, and help prevent corrosion, but low enough to avoid scaling and clouding of hard water. Pool suppliers' recommendations concerning total alkalinity vary widely, but most of these recommendations fall within the range of 80-150 ppm (parts per million) of alkalinity. The higher ranges are recommended when the pool water pH will tend to drift down such as during rainy seasons and when acidic sanitizers are used.

A Guide to Balancing Pool Water