Adjusted Total Alkalinity (aTA) is a refined version of your Total Alkalinity reading that accounts for the portion of alkalinity contributed by cyanuric acid (CYA). When cyanuric acid is present in your pool, it creates a form of alkalinity that does not help buffer your pH the same way carbonate alkalinity does. If not accounted for, it can interfere with accurate LSI calculations and water balance assessments.
The ideal range for Adjusted TA is the same as standard Total Alkalinity: 80 to 120 ppm.
Why does this matter?
Standard Total Alkalinity test results include all alkaline substances in the water, including cyanurate alkalinity from stabilizer. But cyanurate alkalinity behaves differently from carbonate alkalinity and doesn't contribute meaningfully to pH buffering. If your pool has elevated cyanuric acid levels, your raw TA reading can be misleadingly high, causing your LSI score and water balance recommendations to be off.
Adjusted TA removes the cyanurate contribution so that water balance calculations reflect only the alkalinity that actually buffers your pH.
How is it calculated?
Adjusted TA is derived by subtracting a portion of the cyanuric acid reading from your Total Alkalinity. At typical pool pH levels, approximately one-third of your cyanuric acid level is used for this correction. For example, if your Total Alkalinity reads 110 ppm and your cyanuric acid is 60 ppm, your Adjusted TA would be approximately 90 ppm.
Adjusting Adjusted Total Alkalinity
If your Adjusted TA is low after accounting for cyanuric acid, you can raise it with sodium bicarbonate. If it is high, a pH decreaser (muriatic acid or sodium bisulfate) can be used to bring it down. Keep in mind that lowering cyanuric acid, typically by diluting pool water, will also improve the accuracy of your TA readings over time.
The Crystal Water Monitor uses your cyanuric acid reading alongside your Total Alkalinity to calculate Adjusted TA, ensuring that the water balance recommendations you receive are as accurate as possible.