by Rudy Stankowitz, CEO/President, Aquatic Facility Training and Consultants, Pool Man, Educational Consultant, Teaches pool operations & water chem globally, author, and has a podcast.
As much as I’d rather not have to adjust pH in swimming pools as frequently as pH requires adjustment, it is simply a part of pool water chemistry.
There is a lot of talk recently about letting the pH of pool water ‘seek’ its own level and Henry’s law where the science is misrepresented. Firstly, Henry’s law constants are extremely temperature dependent. Secondly, Henry’s law is not applicable when the gas and the solution participate in chemical reactions with each other, such as CO₂ & H₂O.
This is not to mention the preference of algae to colonize in water that has a pH on the higher side of the acceptable range & CH on the higher side of the ideal range.
A pool with a cyanuric acid level present will see a greater loss of chlorine at a pH on the high side of the acceptable range than on the lower side as a greater percentage of hypochlorite ion (which has no bond to CyA) will form. The hypochlorite ion will recognize excessive loss due to UV degradation. At a pH on the lower side of the acceptable range you will see a higher percentage of HOCl which will see CyA protection from the sun’s UV rays.
Remember, LSI is used only as a tool to aid in the protection of the pool itself. If you are going to protect the vessel and ensure water quality without using more chlorine than is necessary you got to look at the whole shabang, not just a small portion of it. All false chemistry must be weeded out and all possible shortcomings must be taken into consideration.