What pH is

It measures whether the water is acidic or basic, from 0 to 14. In a pool the target is 7.2–7.6, the range where chlorine works best and the water doesn't irritate.

  • High pH (>7.6): chlorine loses effectiveness, scale forms and the water turns cloudy.
  • Low pH (<7.2): corrodes metal and seals, irritates eyes and skin.

What alkalinity is

It's the "reserve" that stabilizes the pH. Target 80–120 ppm. With the right alkalinity, the pH stops swinging.

How to adjust them

  • Raise alkalinity: sodium bicarbonate (baking soda). Raises alkalinity with almost no effect on pH.
  • Lower alkalinity: pH reducer (acid), added at one spot without filtering for a few minutes.
  • Raise pH: pH increaser (soda ash) or simply aerate the water (fountains, jets).
  • Lower pH: pH reducer (pH-minus).

Tip

If the pH keeps rising, it's almost always because the alkalinity is high. Fix the alkalinity first and the pH will settle on its own.