Establishing good pool water chemistry standards helps provide guidance for proper water care, and to help ensure that pool water is safe for all swimmers. But some standards are overly restrictive, and the pH range is one of them. For example, there should NOT be a mandate for closing-down swimming pools when the pH is 8.0 to 8.5.
Starting sixty years ago, some pool industry chemists (incorrectly) suggested that a pH of 8.0 and higher makes chlorine ineffective and unsafe to swim in. Not true. Just 1 ppm of chlorine in pool water with a pH of 8.5 and zero CYA contains more active chlorine (HOCl) than needed to kill algae. It should be noted that the common HOCl/OCl/pH percent charts are irrelevant and misleading for pool water containing CYA.
Today, thanks to several chemists, it is now understood that CYA, not pH, is what significantly affects chlorine efficacy in stabilized pools. But some industry people seem to be misinterpreting or not understanding that science and still seem to think that when pool water contains CYA, a pH above 7.8 significantly prevents chlorine from sanitizing. It is also believed by some that raising the chlorine level will not help overcome the effects of higher CYA levels and improve sanitizing effectiveness. Both of those beliefs are false.
One way to explain this is to consider that water with 3 ppm of chlorine at pH 8.5 has more killing power than 2 ppm of chlorine at pH 7.5 when both contain 50 ppm of CYA. Plus, there is 1 ppm extra of chlorine in reserve if needed. That should help illustrate that a pH above 7.8 does not prevent chlorine from properly sanitizing pool water.
There is also more (HOCl) killing power with 4 ppm of chlorine with 80 ppm of CYA than there is with 2 ppm of chlorine at 50 ppm of CYA.
Now, back to the issue of the industry’s mandate to close pools when the pH is above 7.8. Why? We now know that the 7.8 maximum pH was based on incorrect science and assumptions. We know that tap water, serving millions of people, has pH levels above 8.0 and up to 9.3. The always restrictive EPA allows a pH up to 8.5 for drinking water.
Some believe that there is greater eye irritation at a pH of 8.0 than at a pH of 7.0. That belief has been debunked by a peer-reviewed study showing that lowering the pH from 8.0 to 7.0 increased the frequency of eye irritation. That study also stated that raising the pH to 9.0 did not increase eye irritation.
It is known that the (natural) pH of water containing carbonate alkalinity of at least 60 ppm will want to rise to 8.0 – 8.2, and up to 8.5 if the alkalinity is 140 ppm to 180 ppm. Interestingly, the pH at those alkalinity levels do not want to go higher than that.
It is also known that a prominent pool chemistry instructor, the late Jock Hamilton, publicly advocated the concept and benefits of maintaining the pH from 7.8 to 8.2 back in the 1980’s. In fact, many pool service companies have maintained the pH above 7.8 on tens of thousands of pools since the 1970’s without reports of disease, algae outbreaks, eye irritation, or cloudy water resulting from high pH.
Given the above, this likely means that millions of pools across the country often have a pH above 7.8 without sanitation issues. Therefore, if the LSI stays within the balanced range, why fight that tendency of a pH continually rising above 7.8, and continually add acid (to lower the pH) and then add sodium bicarbonate to replace the lost alkalinity that is consumed by the acid?
Therefore, why restrict those who have experienced success and prefer the ease and increased stability of maintaining a higher pH level of up to 8.2 and 8.3? Why sound a false alarm to pool owners that their pool water is out-of-balance and unsafe when it is not? That simply undermines service techs unfairly.
Dr. Stan Pickens has written a scientific research paper on this topic which can be viewed by clicking on this link. http://www.poolhelp.com/wp-content/uploads/2019/03/JSPSI-Volume-6-Number-1-pp-06- 19-Pickins.pdf