High pH in the pool: how to lower it
The ideal pH is between 7.2 and 7.8, best around 7.4–7.5. Above 7.8 chlorine works at half strength, the water clouds more easily and limescale builds up. Below 7.0 the water irritates eyes and skin and damages metal parts.
How much pH minus to add
With granular pH minus (sodium bisulphate), the best-selling product:
- about 90 g per 10 m³ to lower the pH by 0.1, with alkalinity around 100;
- the higher the alkalinity, the more you need: with alkalinity 150 you need about 135 g.
| From → to, in 10 m³ | Alkalinity 100 | Alkalinity 150 |
|---|---|---|
| 7.8 → 7.4 | about 360 g | about 540 g |
| 7.6 → 7.4 | about 180 g | about 270 g |
The manufacturer Bayrol states 100 g per 10 m³ per 0.1. We start a little lower and ask you to retest, because overshooting is worse.
Why in small steps
Don't move the pH by more than 0.4 at a time. If you start at 8.2, the first dose takes you to 7.8. Wait 30 minutes with the pump running, retest and only then add the second. Strips and kits have a margin of error, and acid poured in all at once can drop too far.
How to do it:
1. Pump running. 2. Dissolve the granules in a bucket of pool water (product into water, never the other way round). 3. Pour away from the walls, spreading it out. 4. Wait 30 minutes and retest.
Alkalinity, the pH "buffer"
Alkalinity holds the pH steady. If it's too low (below 60–70) the pH swings. If it's too high (above 150) the pH keeps rising and you need much more acid. In that case bring the pH to 7.0 with acid and then let the water "breathe" (return jet pointing up, a waterfall), repeating every day until the alkalinity drops.
The pH always rises: is that normal?
Yes, with liquid chlorine, with salt chlorination and with waterfalls and water features. Air makes the pH rise. What to do:
- keep alkalinity low, between 60 and 80;
- correct every 2–3 days with small doses instead of one big dose a week;
- point the return jet downwards.
Before a shock treatment
If you need to shock (green water, chlorine smell), bring the pH to 7.2 even if it's "in range". Chlorine works much better.
Safety
Chlorine and pH minus never together: dose them at different times and in different places, never in enclosed spaces. Together they make toxic gas.
Let Serenpool do the maths
Enter pH and alkalinity: Serenpool works out the dose for your pool, splits it into safe steps and reminds you when to retest.
Indicative doses calculated from public formulas and manufacturers' data sheets. Always check your product's label.