For at least 40 years, many pool service companies have been successfully maintaining their residential pools on a once-a-week visitation basis. Empirical evidence has shown that pool water can be kept safe and properly sanitized without harmful bacteria and algae developing with weekly treatment programs.
Also, pool service companies provide a great service by keeping hazardous chemicals out of the hands of pool owners and their children.
One reason that pools can be kept properly sanitized with weekly visits is due to the use of various feed or auto-systems which usually use either bleach, Cal hypo, Salt, Trichlor, or bromine for sanitizing. And of course, the use of Ozone and UV systems also keep pool water safe without daily treatments.
The use of cyanuric acid, which slows down chlorine loss, also helps to provide the ability for less frequent chemical treatments. In fact, there are no reports or studies that suggest that professional once-per-week treatments automatically result in unsafe, cloudy, or algae pool water conditions.
Another important aspect of maintaining a good chemical and sanitizing program for residential pools is maintaining the pH within a proper range. One thing that worries some service techs is when pH drifts higher in the days between service visits.
In that regard, some service techs and others in our industry seem to believe that a pH of 8.0 to 8.4 makes chlorine in pool water completely ineffective and unable to properly sanitize and kill bacteria and algae. It is also incorrectly taught that eye and skin irritation develops at these pH levels. Both of those concepts are not true.
It is well known that CYA reduces the amount of “active” hypochlorous acid (HOCl) in the water. But what is not well-known is that when the pH rises slightly in pools containing CYA, the amount of HOCl almost remains the same, and therefore, has nearly the same sanitizing efficacy and bacteria killing power.
In 1974, a report written by J. E. O’Brien indicated that when the pH rises from 7.5 to 7.8, the reduction in HOCl only drops by about 10%, and when the pH rises from 7.8 to 8.2, the reduction in HOCl only drops by 10% also.
But is that the end of the story? What about that lower amount of active chlorine? Is the water unsafe? While a 10% lower amount of HOCl wouldn’t make a lot of difference in sanitizing, the lower amount of HOCl can be easily compensated for and overcome by simply maintaining the chlorine 10% higher.
For example, pool water with 2 ppm of chlorine, with 50 ppm of CYA, and at a pH of 7.8 is considered acceptable by industry standards. All one needs to do to obtain the same killing power and chlorine efficacy when the pH is maintained at 8.2, is to raise the chlorine level by 10% or to 2.2 ppm. Obviously, that isn’t very much additional chlorine in a 15,000-gallon residential pool. Only about 3.2 ounces of pool bleach.
Let’s also understand that if the chlorine is at 3 ppm in the above example with a pH of 8.2, it means that there is more sanitizing (killing) efficacy than having the chlorine at 2 ppm with a pH of 7.5, or even at a pH of 7.2. This example shows that pool water can be better sanitized at a pH of 8.2 (due to higher chlorine levels), and a higher pH does not automatically render chlorine incapable of killing bacteria and algae.
Plus maintaining the chlorine level a little higher results in a higher reservoir of OCl- ready to convert into the more active HOCl.
Finally, studies have shown that a pH of 8.0 to 8.4 alone does not cause eye and skin irritation. So service techs can stop fretting about a pH rising above 7.8 between visits. In fact, many pool service companies have been successfully maintaining the pH from 7.8 to 8.2 for many years.