The Orenda Calculator pH dials only go up to 8.5 on the left, and 8.2 on the right. And it's by design.
The Orenda Calculator only goes up to 8.5 on the left because that is the maximum pH that accurate calculations can be made with. The pH dial on the right is maxed at 8.2 because no matter what your circumstance, keeping pH below 8.3 is always recommended in swimming pools, provided you are not going red on the LSI (below -0.30).
Maximum pH for accurate calculations
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 that has 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.
Above 8.5 pH, the math involved becomes more complex, and accuracy drops. We do realize that pools can get over 8.5 when forced (i.e. etching or an algae bloom), but generally we want to get the pH back below that no matter what. That often involves reducing alkalinity, and sometimes calcium hardness to maintain LSI balance (to offset the reduced alkalinity).
Why 8.2 maximum on the right dial?
To best explain why we decided to cap the pH dial at 8.2 on the right side of our calculator, some context is helpful. See the pH buffer equilibria in the chart below:
Look at 8.3 pH. At 8.3 pH, bicarbonate ions convert into carbonate ions. Its best to avoid that, because when free carbonates are in the water, they will find calcium and form calcium carbonate. This calcium carbonate will precipitate out of solution and form either scale, dust, or carbonate clouding. It's best to stay below that threshold and manage the LSI.
We decided to limit the pH on the right to show users their LSI at the maximum pH below that threshold (8.2).
So that's why we limit the dials: accuracy and to help protect users (and their pools) from scale and carbonate clouding issues.