Pool & Spa
The Trusted Choice for Balanced Water
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 Association of Pool & Spa Professionals (APSP) 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 tri-chloramines. 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 is essentially a measure of dissolved bicarbonates in water. It is also a measure of the ability of water to resist changes in pH when acids (low pH) or bases (high pH) are added.
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, as in rainy seasons, and when acidic sanitizers are used.
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 to 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.
The Relationship Between Pool pH & Alkalinity
Research studies have shown that there is clearly a relationship between pool pH and total alkalinity present in water. 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.
The Association of Pool & Spa Professionals recommends maintaining the available chlorine level between 1.0 and 3.0 ppm. If there is less than 0.6 ppm of chlorine, there may not be sufficient disinfecting power to kill pathogens, resulting in the build-up of unpleasant odors and eye-irritating chloramines. If too much chlorine is added, it is a waste of 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.
Our Alkalinity First™ Dosing Chart
Pool and spa operators and owners should test for alkalinity regularly, and the amount of alkalinity increaser needed to raise alkalinity is easily calculated utilizing the chart below.
When total alkalinity testing is not available, it is still possible to safely increase the value to a more optimal level by using a pH test as a guide. If the pH is less than 7.2, the total alkalinity of the pool water will likely always be below 70 ppm. In this case, add at least 60 ppm of alkalinity.
Adding 9 pounds of Alkalinity First™ for each 10,000 gallons of pool water will raise the total alkalinity by 60 ppm, which will usually raise the pH of the pool water into the desirable range of 7.2 to 7.8.