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The pH is a measure of the acidity or alkalinity of the water. In pools, pH should be maintained at 7.4 to 7.6 ppm for optimal sanitiser activity, protection of pool surfaces, and bather comfort.

If the pH drops below 7.4, the water is too acidic. This can corrode pool surfaces and equipment and cause burning eyes and skin irritation for bathers. To raise pH, add Balance Pak 200 according to label instructions.

If the pH above 7.6, the water is too alkaline. The sanitiser loses some effectiveness, and minerals can fall out of solution, causing cloudy water, scale buildup, and equipment and surface damage. To lower pH, add Lo'N'Slo or liquid acid (hydrochloric acid, muriatic acid).

Various environmental factors can affect pH, such as airborne contaminants, rain, fill water, pollutants, and swimmers. Other products that are added to the pool for sanitation, oxidation, and balancing can also effect pH. The pH is lowered by the use of products such as trichlor tablets, acid rain, and other environmental contaminants. The pH is raised by use of some shock products as well as swimmers. The ALEX water analysis recommendations take into account the effect that any product it recommends will have on the pH. This is why, in some cases, ALEX may recommend Lo'N'Slo when the pH is already low. Some other product has been recommended that will raise the pH too high, and this is taken into account in the final pH adjustment.

Since the pH changes frequently due to these outside influences, it should be tested at least twice weekly. Make any necessary adjustments to raise or lower it to the proper range. To raise pH, use Balance Pak 200. To lower pH, use Lo'N'Slo.

Bicarbonate Scale and low pH:

If the pH is low and does not respond to additions of increaser, check the total alkalinity. If the total alkalinity is high and increasing, the problem could be bicarbonate scale. This occurs when pools are not allowed to gas off properly. Trapped gases from solar covers or poor ventilation in indoor pools are reabsorbed into the water and drive the pH down and the total alkalinity up. It can also cause the water to cloud. It is necessary to remove the cover during next few days while rebalancing the pool. If there is no cover, but the pool is indoor, ventilate the room as well as possible.

Chlorine demand and low pH:

Another cause of persistently low pH is chlorine demand. If the pool has a chlorine demand the pH usually stays around 7.2. When the demand is satisfied, the pH can be adjusted.