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The Future for pH and Chlorine Standards

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It appears that the pool industry’s long-time recommended parameters for chlorine and pH levels will be changing in the near future.

The current range of 1 to 4 ppm for chlorine will likely be raised when pool water contains cyanuric acid (CYA), and the pH range will be broadened beyond the current limited range of 7.2 to 7.8. The reason for this change is due to a new understanding of the science of stabilized pool water.

Some years ago, Richard Falk (known as Chemgeek on pool forums) wrote about the relationship between CYA, Chlorine, and pH, and communicated that information to the Council for the Model Aquatic Health Code (CMAHC) that adopts standards for public and commercial pools. As a result, two years ago the CMAHC formed an Ad-Hoc committee with Ph.D. chemists, micro biologists, and other knowledgeable industry members to study that topic.

At the recent World Aquatic Health Conference in October, Richard Falk, representing the CMAHC Ad-Hoc committee, presented scientific data regarding the benefits of CYA and on the chlorine/CYA/pH equilibrium relationships, including bacterial kill rates, and other factors affecting pool sanitizing by chlorine when CYA is present.

To summarize, the CMAHC is tentatively suggesting higher minimum amounts of Free Chlorine should be maintain and proportionately based on the amount of CYA present in pool water. For example, at 40 ppm of CYA, the minimum Free Chlorine level should be at least 2 ppm, and at a CYA level of 90 ppm, the minimum chlorine level should be 4.5 ppm.

It should be noted that the CMAHC is aware of the EPA’s chlorine regulation minimum of 1 ppm and maximum of 4 ppm. However, the CMAHC believes that higher Free Chlorine levels are necessary to achieve safer and healthier pool water. Also mentioned was that a higher pH (above 7.8) does not significantly affect chlorine efficacy (killing power) when CYA is present.

It was clear from statements made by various CMAHC and CDC representatives that standards should be adjusted or changed as science becomes better understood. They also emphasized that flexibility in standards are needed (when scientifically supported) to allow more effective water maintenance.

At some point, the CMAHC and CDC will probably present this science to the EPA in hopes that higher chlorine levels will be adopted when CYA is present. And a broader pH range (due to applicable science) may be forthcoming also.
For more information and a simplified explanation of the science regarding Chlorine/pH Efficacy when CYA is present in pool water, see this link:

Dr. Stan Pickens (Ph.D. and water chemistry consultant) has also written a very detailed and scientific paper on “Relative Effects of Chlorine and pH on Disinfection” which will also be available to read.

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Comment by Kevin Misley on February 7, 2018 at 11:18am

OK Thanks Kim for the information and the hard work.

Please continue posting information as it comes available.

Comment by Kim Skinner on February 7, 2018 at 10:04am

And as far as pH is concerned, the science shows that a higher than 7.8 and up to at least 8.2 should be allowed. And that should apply to pools with and without CYA.  There is still plenty of chlorine killing power at a pH of 8.2 without CYA, and makes little difference with CYA use. 


Comment by Kim Skinner on February 7, 2018 at 9:44am

I personally think that indoor pools should be allowed to maintain CYA levels at about 20 to 25 ppm if desired. Having said that, I am fairly certain that if the CYA is zero, then the suggested and appropriate chlorine level should remain at the current standard of 1 to 4 ppm of chlorine.

Comment by Kevin Misley on February 7, 2018 at 8:01am


I'm wondering what the suggested parameters are for indoor pools where the CYA is to be 0? Either public or residential?

Comment by John on December 16, 2017 at 5:36am

I would also like to thank you for you very thought provoking posts. I take time to interpret what you say as it doesn't always immediately seem to be possible.  Then there is Ben Powell, an original thinker on pool chemistry and the guy with the best guess chlorine CYA chart. I noticed similar regarding the strength in PPM with CYA and chlorine and it became a lot clearer when Richard introduced me to Ben's work.

Not sure how this will be received in Europe as Germany has a tight DIN standard and utilises ph7-7.2 for pool but much better filtration than other countries. Time will tell.

Comment by Kim Skinner on December 14, 2017 at 6:22pm

Thank you John.

Yes, we owe Richard a thanks. This will be a good step upward and is needed for our industry. I hope there isn't too much of a resistance from the big companies to changing these parameters. But the science is the science.      


Comment by John on December 14, 2017 at 3:24am

Thanks for the update Kim, well done to Richard for pursuing this over the years and to keep pushing for a better understanding. One small step for a man, one giant leap for the industry!

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