What is the pH value in the pool and why is it so important?
The pH value is one of the most important parameters for clean and healthy pool water. It indicates whether the water is acidic (pH < 7), neutral (pH = 7) or alkaline (pH > 7). The optimum pH value for pool water is between 7.2 and 7.6.
Why is this range so important? If the pH value is too low or too high, the following problems can occur:
- Skin irritation and reddening of the eyes in bathers
- Reduced disinfection effect of chlorine
- Corrosion of metal surfaces and pool equipment
- Turbidity of the water and algae formation
- Limescale deposits if the pH value is too high
Pool: What is the optimum pH value?
DIN 19643 (German standard for swimming and bathing pool water) defines the optimum pH range for pool water as between 7.0 and 7.4. In practice, however, the range 7.2 to 7.6 has proven to be ideal, as it:
- Maximum chlorine effectiveness guaranteed (chlorine is 66% effective at pH 7.2)
- is skin-friendly and corresponds to the natural pH value of human tear fluid (7.2-7.4)
- Prevents corrosion and limescale deposits
- Ensures clear water quality
pH value table for pool water
| pH value | Evaluation | Effects |
|---|---|---|
| < 6,8 | ❌ Too acidic | Corrosion, skin/eye irritation, chlorine degradation |
| 6,8 – 7,0 | ⚠️ Limit range | Suboptimal, should be raised |
| 7,0 – 7,4 | Optimal (DIN 19643) | Ideal conditions |
| 7,2 – 7,6 | ✅ Ideal (practice) | Best balance of disinfection & comfort |
| 7,6 – 7,8 | ⚠️ Limit range | Chlorine effect decreases, limescale formation begins |
| > 7,8 | ❌ Too alkaline | Chlorine ineffective, turbidity, limescale deposits |
Measuring the pool pH value: how to do it correctly
There are three common methods for measuring the pH value in the pool:
1st test strip (quick & easy)
Pros: Inexpensive (approx. €10-20 for 50 strips), easy to use, quick result
Disadvantages: Less precise (±0.2-0.5 pH units), note expiration date
Application: immerse strips in water for 2-3 seconds, compare with color scale after 15 seconds
2. liquid tests with reagents (more precise)
Advantages: More accurate than test strips (±0.1-0.2 pH), reliable
Disadvantages: More expensive, reagents have expiration date
Application: Take water sample, add reagent, compare color with scale
3. digital pH meters (professional)
Advantages: Very precise (±0.01 pH), direct display, no color interpretation
Disadvantages: More expensive (50-200€), regular calibration necessary
Application: Hold electrode in water, read digital value
When and where to measure?
- Frequency: At least 2-3 times a week, daily for intensive use
- Time: In the morning or evening (not in direct sunlight)
- Location: At elbow depth (approx. 30-40 cm below the surface), away from inlet nozzles
- After adding chemicals: wait 4-6 hours, then measure again
Pool chlorine value: correlation with the pH value
The pH value and the chlorine content in the pool are closely linked. Chlorine is only effective at an optimum pH value!
Chlorine effectiveness depending on the pH value:
- pH 7.0: Chlorine 73% effective
- pH 7.2: Chlorine 66% effective (optimal)
- pH 7.4: chlorine 50% effective
- pH 7.6: chlorine 33% effective
- pH 8.0: Chlorine only 20% effective
Conclusion: A pH value of 7.8 or higher means that disinfection will no longer work properly even if the chlorine content is sufficient!
Optimum chlorine values for pools:
- Free chlorine: 0.5 – 1.0 mg/l (ppm) for private pools
- Public swimming pools: 0.3 – 0.6 mg/l (DIN 19643)
- After shock chlorination: Briefly up to 3-5 mg/l, then lower again
Lowering the pH value in the pool: how it works
If the pH value is above 7.6, it must be lowered. Here are the common methods:
pH-Minus (granules or liquid)
Active ingredient: Sodium hydrogen sulphate or hydrochloric acid
Dosage: According to manufacturer’s instructions (approx. 100g pH-Minus per 10m³ lowers pH by 0.1)
Application:
- Switch on the pool pump (for circulation)
- Add pH-Minus in portions to the water (with the pump running)
- Wait 4-6 hours
- Measure pH again and readjust if necessary
⚠️ Important: Never add pH-Minus and chlorine at the same time! Keep at least 4 hours apart.
Natural methods (for minor corrections)
- CO₂ addition: lowers pH gently (professional systems)
- Rainwater: usually has a lower pH value (5-6)
Increase the pH value in the pool: If the water is too acidic
If the pH value is below 7.0, the value must be raised:
pH-Plus (granules or liquid)
Active ingredient: Sodium carbonate (soda)
Dosage: Approx. 100g pH-Plus per 10m³ raises pH by 0.1
Application: As for pH-Minus (in portions, pump on, wait 4-6h)
Natural alternatives:
- Baking soda (sodium hydrogen carbonate): Gentler than pH-Plus, good for slight increases
- Soda (washing soda): Stronger than baking soda, cheaper
pH value fluctuates in the pool: common causes
If the pH value is constantly out of balance, the following factors may be the cause:
- Rainwater: lowers the pH value (is usually acidic)
- Lots of bathing: body oils, sweat, cosmetics increase pH
- Fresh water refill: Depending on tap water quality
- Algicides & chlorine: Can influence pH
- Low alkalinity (TA value): Buffer function is missing
Solution: Stabilize TA value (total alkalinity)
The TA value should be between 80-120 mg/l. It buffers pH fluctuations. TA value too low → pH fluctuates greatly!
Increase: Add sodium hydrogen carbonate (baking soda)
Decrease: Use pH-Minus (also lowers TA)
Professional pool test: when to go to the lab?
Quick tests at home are practical, but not always sufficient. In the following cases, we recommend a professional pool water analysis in an accredited laboratory:
- Public swimming pools: Legal obligation (DIN 19643) – regular sampling required
- Permanent problems: turbidity, algae, despite correct values
- After refilling: Check the water quality of the tap water
- Health complaints: Skin irritation, redness of the eyes despite “normal” values
- Suspected contamination: e.g. after storms, construction work
Professional pool test: when to go to the lab?
A professional pool water analysis includes, among other things
- pH value (high-precision measurement)
- Free & combined chlorine
- Alkalinity (TA value)
- Calcium hardness
- Total hardness
- Cyanuric acid (when using chlorine stabilizers)
- Microbiological parameters (E. coli, Legionella, Pseudomonas aeruginosa)
- Heavy metals (iron, copper, manganese)
A DAkkS-accredited analysis is mandatory for public swimming pools and commercial enterprises!
Conclusion: pH value pool - the key to clean water
The optimum pH value of 7.2 to 7.6 is the basis for hygienically perfect and pleasant pool water. Regular measurement (2-3 times/week) and rapid correction in the event of deviations are essential.
The most important points at a glance:
- Ideal pH value: 7.2 – 7.6
- Measure regularly: At least 2-3x per week
- First adjust pH, then add chlorine (4-6h interval)
- Keep TA value (alkalinity) at 80-120 mg/l
- For permanent problems: Professional laboratory analysis
Professional pool water analysis at FADER Umweltanalytik
Do you operate a public swimming pool, a hotel pool or do you have problems with the water quality? The DAkkS-accredited FADER laboratory in Karlsruhe offers professional pool water analyses in accordance with DIN 19643:
- Chemical & microbiological parameters
- Quick results & recommendations for action
- Sampling service for commercial enterprises
- ISO 17025 accredited
Request a pool water analysis now →
Note: This article is for information purposes only. Public swimming pools are subject to legal requirements (DIN 19643), which require regular professional analysis by an accredited laboratory.
Frequently asked questions (FAQ)
How often should the pH value in the pool be measured?
At least 2-3 times a week. In case of intensive use, after rainfall or the addition of chemicals, measure daily.
What happens if the pH value is too high?
At pH > 7.8, chlorine becomes ineffective, the water becomes cloudy, limescale deposits form and skin irritation is possible. The pH value must then be lowered with pH-Minus.
Can I adjust the pH value and chlorine at the same time?
No! Always correct the pH value first, then wait 4-6 hours and only then add chlorine. Otherwise both agents may lose their effect or hazardous gases may be produced.
Why is the pH value in the pool constantly rising?
Common causes: Low alkalinity (TA value too low), many bathers, algae growth, or hard tap water. Check the TA value and stabilize it at 80-120 mg/l.
Is a digital pH meter better than test strips?
Yes, digital meters are more precise (±0.01 pH vs. ±0.5 pH with test strips). Test strips are usually sufficient for home use. For public pools or permanent problems, digital devices or laboratory tests are recommended.
What is the ideal pH value for saltwater pools?
The following also applies to saltwater pools: 7.2 to 7.6. Saltwater chlorine generators work best at this pH value.