The Orenda Calculator's pH dials only show from 4.0 to 10.5 pH. And it's by design.
The Orenda Calculator™ only shows between 4.0 and 10.5 because of the practical minimum and maximum pH extremes we might encounter in swimming pool chemistry.
Of course, we don't want such pH extremes, but there are circumstances in pool care that exist. Namely, hot starts have a pH below 4.3, and green pools tend to be about 10.3 to 10.4 pH.
The importance of pH in swimming pool chemistry
pH impacts most of the other factors in water chemistry. When calculating things like the LSI, carbonate alkalinity, and pH ceiling, pH affects all of those directly. Specifically, pH changes the multiplier associated with Cyanuric Acid (CYA) and Borate when correcting against total alkalinity to calculate carbonate alkalinity. The higher the pH, the more significant the Borate and CYA corrections. The lower the pH, the less significant those corrections become.
For the LSI, pH is the only factor with no multiplier. It is directly inputted into the calculation. And when using the Orenda Calculator, you will see how much of an impact changing the pH has on the LSI.
Why is 4.0 the minimum pH on the Orenda Calculator™?
While we strongly recommend against the practice, many pool companies still do acid startups on plaster pools, aka a "zero-alkalinity startup" or a "hot start". A hot start is not a startup strategy; it is an exposure method. It burns through cement and dissolves it into the water to hopefully make the pool look better.
In order to achieve zero alkalinity, the pH must be dropped below 4.3. So we made our minimum 4.0 pH. Sure, too much acid can drop the pH below 4.0, but this is a short, temporary process (hopefully!), and sodium bicarbonate or soda ash will neutralize the acid after a day or two.
Why is 10.5 the maximum pH on the Orenda Calculator™?
Hopefully, your swimming pool never gets to 10.5 pH. But during a new plaster startup–especially if you are not managing the LSI during the fill–pH can spike as water dissolves calcium from the cement. The pH of calcium hydroxide is 12.6, but water only takes a small amount of it until the water's LSI is balanced. So, we typically do not see a pH above 10.5 on a startup.
If you are doing our Orenda Startup™ process, the pH should not spike in the first place because the water is not capable of stealing calcium from the cement.
The other reason for 10.5 is for green pools that are full of algae. Algae are plants that consume carbon dioxide (CO2), which increases the pH. We have digitally tested the pH of several green pools, and they are usually in the low 10's. So, we made our maximum 10.5 on the calculator.
