Total alkalinity in a pool: the buffer that stabilises the pH
Total alkalinity is the most underrated figure in pool care. It is what stops the pH from swinging in every direction. Understand it, and you stop chasing an unstable pH.
In short
Total alkalinity (TA) measures the water’s buffering power: its ability to resist pH changes. Too low (under 80 mg/L), the pH becomes unstable and yo-yos; too high (above 150 mg/L), the pH locks and resists correction. The sweet spot is around 80 to 120 mg/L. Setting the alkalinity before the pH is the key to stable water.
What total alkalinity does
Think of alkalinity as a shock absorber for the pH. With good alkalinity, the pH takes disturbances (rain, product additions, bathers) without moving much. Without it, the smallest drop of corrector sends the pH plunging or soaring: the exhausting, product-hungry "pH yo-yo".
The right values and how to set them
Aim for about 80 to 120 mg/L. To raise alkalinity that is too low, use an alkalinity increaser or baking soda. To lower alkalinity that is too high, add pH-minus corrector in steps, with filtration running. In all cases: set the alkalinity before the pH.
What to do, step by step
Test the alkalinity
Use a strip or a kit that measures alkalinity. Note the value before any correction.
Correct the alkalinity first
Too low: alkalinity increaser or baking soda. Too high: pH minus in small steps.
Then adjust the pH
Once the alkalinity is in range, the pH stabilises far more easily.
Recheck after rain
Heavy rain lowers the alkalinity: check it after a storm.
Frequently asked questions
What is the right alkalinity value?
About 80 to 120 mg/L. Below 80, the pH becomes unstable; above 150, it locks and resists correction.
Should I set the alkalinity or the pH first?
The alkalinity first, always. It is what stabilises the pH: without correct alkalinity, any pH adjustment is short-lived.
What is the difference between alkalinity and pH?
The pH measures the water’s acidity; alkalinity measures its ability to resist pH changes. They are linked, but it is the alkalinity that keeps the pH stable.