Pool pH too low: how to raise it lastingly
A pH below 7.0 makes water corrosive: it stings the eyes, damages the liner and the equipment. Before adding pH plus, you often need to look at the total alkalinity — that is what explains a pH that keeps dropping.
In short
A pH that is too low attacks the liner, metal parts and swimming comfort. You raise it with a pH-plus corrector, but the real key is the total alkalinity (the water’s buffering power): when it is too low, the pH becomes unstable and drops back constantly — the "pH yo-yo" effect. So you correct the alkalinity first, then the pH.
Why a low pH is a problem
Below 7.0, the water becomes acidic and aggressive. Typical effects: irritated eyes and skin, a liner that weakens, and metal parts (ladder, screws, heat-pump exchanger) that corrode. A well-set pH, between 7.0 and 7.4, protects both bathers and the installation.
The hidden cause: alkalinity
Total alkalinity is the water’s buffering power: it is what stabilises the pH. When it drops below about 80 mg/L, the pH has nothing left to anchor it and swings wildly at the slightest addition of product or after rain: this is the "pH yo-yo". Raising the pH without correcting the alkalinity never lasts long.
Common triggers
Heavy rain (rainwater is naturally acidic and lowers both pH and alkalinity), an excessive addition of pH-minus corrector, or naturally soft top-up water are the most common causes of a plunging pH.
What to do, step by step
Measure the pH and alkalinity together
Never look at the pH alone. If the alkalinity is under 80 mg/L, that is the priority.
Correct the alkalinity first if needed
If alkalinity is too low, raise it with an alkalinity increaser before touching the pH. The pH will then stabilise far more easily.
Raise the pH with pH plus
Add the pH-plus corrector gradually, with filtration running, following the doses stated on your product label.
Let it circulate, then retest
Wait a few hours of filtration before retesting, to let the product disperse. Adjust again if needed, in small amounts.
Frequently asked questions
What are the effects of low pH in a pool?
Acidic, corrosive water: stinging eyes and skin, a weakened liner, and metal parts (ladder, screws, heat-pump exchanger) that corrode. Bringing the pH back to 7.0–7.4 protects both swimmers and equipment.
How do I raise the pH in a pool?
With a pH plus corrector (sodium carbonate), added gradually with filtration running, after checking the alkalinity. Our pH plus dosage calculator estimates the amount from your volume and the gap to close.
What is the right pH for a pool?
Between 7.0 and 7.4. In that range, chlorine is effective and the water stays comfortable and non-corrosive.
Why does my pH keep dropping?
Almost always because the total alkalinity is too low: without enough buffering, the pH becomes unstable and falls back. Correct the alkalinity and the pH will hold.
What about the pH after a big storm?
Rainwater is acidic and lowers both the pH and the alkalinity. After a storm, always test both and rebalance if needed.