Home › Pool Advice & Guides › Balancing your pH
The parameter to set before anything else
pH is one of the first parameters to watch in a pool. When it is properly set, everything else in the treatment becomes much easier to manage. Here is, concretely, why and how to check and correct it.
1 · pH in 30 seconds
pH measures the balance between the acidic and basic nature of the water, on a scale from 0 to 14. Below 7, the water is acidic; above, it is basic.
For a chlorine-treated pool, you want water that is very slightly basic, most often between 7.0 and 7.4, with a practical target often around 7.2. The ideal value can vary depending on your treatment and equipment: refer to the instructions for your products and equipment.
Keep in mind: pH is not a secondary reading, it is the parameter to watch as a priority.
2 · Why your pH keeps changing
Almost every owner asks this question. Pool pH is not a value you set once for the whole season: it changes naturally with…
- adding fresh water;
- high heat and evaporation;
- rain, sometimes acidic;
- how much the pool is used;
- certain treatment products;
- the use of a salt chlorinator, which tends to raise the pH;
- the water's overall balance (hardness, alkalinity / TAC).
3 · Why won't my pH "hold"? The role of TAC
If your pH keeps rising or falling despite your corrections, the cause is oftenalkalinity (TAC). TAC is the water's ability to buffer pH changes: it is what "holds" the pH in place.
When TAC is too low, the pH becomes unstable and swings at the slightest cause. When it is too high, the pH becomes, on the contrary, very hard to bring down. Lastingly balancing your pH therefore often starts with a correct TAC.
4 · pH too low, balanced or too high
| pH too low (acidic water) | balanced pH | pH too high (basic water) |
|---|---|---|
| More aggressive water | Properly balanced water | Water more likely to encourage deposits |
| May encourage irritation | Comfortable swimming | Water that can turn cloudy |
| May encourage corrosion of some materials | Easier treatment to manage | Chlorine disinfection less favourable |
| Possible attack on some equipment | Good overall balance | Possible scaling |
It should stay nuanced: pH is only one of the parameters of the water balance. These effects are tendencies, not automatic consequences.
5 · The key point: pH commands how well chlorine works
This is the most important message on this page. pH directly influences how chlorine behaves. In water, chlorine exists in two forms in equilibrium:hypochlorous acid (the most active form) and the hypochlorite ion (much less effective). The higher the pH, the smaller the share of the active form.
In other words: with a pH that is too high, you can show a "good" chlorine level and yet have less effective disinfection. Hence the rule: check and correct the pH before multiplying treatments.
- Check the pH
- Correct the pH if needed
- Check the disinfectant (chlorine)
- Check the other parameters
- Enjoy stable, predictable water
6 · How to correct the pH
It is simple in principle, provided you go gradually and let the product act before checking again, with filtration running.
|
◆ pH too high → bring it down With a pH minus (pH-)corrector, in powder or liquid, at the dose stated by the manufacturer. Let the water circulate then check again. |
◆ pH too low → bring it up With a pH plus (pH+)corrector, on the same principle: manufacturer's dose, filtration running, check after circulation. |
7 · Going further: the automatic controller
For a pool fitted with compatible filtration, an automatic controller (dosing pump) measures the pH continuously or at regular intervals and commands the injection of the corrector needed. The principle: measure → compare → correct.
Its value is not only to automate a task: it is to keep a more stable pH day to day, and therefore a more regular treatment with fewer "random" corrections.
See our dosing pumps / pH controllers
8 · Keeping your pH in good shape day to day
Every week
- check the pH;
- check the disinfectant;
- check the filtration;
- look at the water visually.
After a particular event
Check the water again after a heavy storm, heavy use, a large addition of fresh water, a change of treatment or a spell of high heat.
Even with an automatic controller
- check the displayed value regularly;
- check the probe as per the manufacturer;
- check the corrector product level;
- check the pH periodically with an independent measurement;
- watch the pipework and the injection system.
9 · The most common mistakes
- Correcting the chlorine without looking at the pH — the pH must be among the first parameters checked.
- Adding a lot of product at once — follow the manufacturer's dose.
- Measuring the pH only once a month — it changes between two checks.
- Thinking a controller means you no longer maintain the water — it automates pH regulation, not the overall maintenance.
- Mixing products — they are used separately, according to their instructions.
10 · Frequently asked questions about pool pH
What pH should I aim for in a pool?
Most often between 7.0 and 7.4, with a practical target often around 7.2, depending on your treatment and equipment.
Why is my pool's pH rising?
Because of high heat, evaporation, adding fresh water or a salt chlorinator, which tends to push it back up.
Why is my pool's pH falling?
Rain, certain treatment products and the water balance can push it down.
How do I lower the pH?
With a pH minus (pH-) corrector, at the manufacturer's dose, filtration running, then check after circulation.
How do I raise the pH?
With a pH plus (pH+) corrector, on the same principle of gradual dosing.
Why does my pH never hold?
It is often a matter of alkalinity (TAC): a TAC that is too low makes the pH unstable. Check the TAC first.
Should I set the pH before the chlorine?
Yes, it is preferable: pH determines how effective chlorine is, so you correct it as a priority.
How often should I check the pH?
A weekly check is a good baseline, to be stepped up after a storm, heavy use, an addition of fresh water or high heat.
Want more stable water and a pH that is simpler to manage?
See our pH correctors (pH- / pH+)See also
→ Cyanuric acid (stabiliser): how to bring it down
← Back to Pool Advice & Guides
This guide is provided for information only. Always follow the instructions for use of treatment products, and do not mix them with one another. If in doubt about your water balance, ask for advice.