Introduction
pH is the most important parameter in pool water chemistry. This simple number determines chlorine effectiveness, swimmer comfort and equipment longevity. Keeping pH balanced isn't optional - it's essential.
In Margem Sul, the variability of water sources (mains vs. well) creates unique challenges. Some areas have naturally acidic water, others alkaline. Knowing how to test and correct pH allows you to solve most water quality problems.
This practical guide teaches you everything about pH balance: why it's important, how to test, and how to correct it when outside ideal values.
What is pH
Simple Definition
pH measures the acidity or alkalinity of water on a scale of 0 to 14.
| Value | Classification |
|---|---|
| 0-6.9 | Acidic |
| 7.0 | Neutral |
| 7.1-14 | Alkaline (basic) |
Values for Pools
| pH Value | State | Action |
|---|---|---|
| < 7.0 | Very acidic | Urgent correction |
| 7.0-7.2 | Slightly acidic | Adjust |
| **7.2-7.6** | **Ideal** | **Maintain** |
| 7.6-7.8 | Slightly alkaline | Adjust |
| > 7.8 | Very alkaline | Urgent correction |
Why pH is Important
Chlorine Effectiveness
| pH | Chlorine Effectiveness |
|---|---|
| 7.0 | 73% |
| 7.2 | 66% |
| 7.4 | 55% |
| 7.6 | 45% |
| 7.8 | 33% |
| 8.0 | 22% |
💡 Dica Profissional
With pH at 8.0, you need almost triple the chlorine to achieve the same disinfecting effect as at pH 7.2. This means more cost in products and more irritation for swimmers.
Impact on Comfort
| pH | Effects on Swimmers |
|---|---|
| Low (< 7.0) | Red eyes, irritated skin, burning |
| Ideal (7.2-7.6) | Comfortable, no irritation |
| High (> 7.8) | Dry skin, irritated eyes, affected mucous membranes |
Impact on Equipment
| pH | Effects on Equipment |
|---|---|
| Low | Metal corrosion, heater damage, gasket degradation |
| Ideal | Protection, normal lifespan |
| High | Calcification, blockages, deposits |
Impact on Water
| pH | Water Appearance |
|---|---|
| Low | May look normal but is aggressive |
| Ideal | Crystal clear, well balanced |
| High | Cloudy, tendency for limescale |
Factors That Affect pH
Make pH Rise
| Factor | Explanation |
|---|---|
| Sodium hypochlorite (bleach) | Very high pH (12-13) |
| Aeration/jets | Releases CO2 from water |
| Waterfalls/water features | Same reason |
| Mains water (some areas) | Already alkaline |
| Hot weather | Accelerates CO2 release |
Make pH Drop
| Factor | Explanation |
|---|---|
| Chlorine tablets (trichlor) | Low pH (2.8-3) |
| Dichlor | Moderately acidic pH |
| Rain | Generally acidic |
| Swimmers | Sweat, urine (acids) |
| Well water (some areas) | May be naturally acidic |
| Organic matter | Degradation produces acids |
How to Test pH
Testing Methods
| Method | Precision | Cost | Ease |
|---|---|---|---|
| Test strips | ±0.4 | £ | Very easy |
| Liquid reagent kit (phenol) | ±0.2 | ££ | Easy |
| Digital photometer | ±0.1 | £££ | Easy |
| Electronic meter | ±0.1 | ££££ | Calibration needed |
Testing Procedure
1. Collect sample correctly:
- Use clean container
- Collect at 30-50 cm depth
- Away from return jets and skimmer
- Water should have been circulating for at least 1 hour
2. Do the test:
- Follow kit instructions
- Compare colours immediately (strips)
- Or add reagent and compare (liquid kit)
3. Record result:
- Note date, time and value
- Compare with previous tests
- Identify patterns
Testing Frequency
| Situation | Frequency |
|---|---|
| Normal use | 2-3 times per week |
| Intensive use | Daily |
| After adding products | 4 hours later |
| After heavy rain | As soon as possible |
| Recurring problems | Daily |
💡 Dica Profissional
Always test pH before adding other chemicals. If pH is well outside ideal, correct it first and only then add chlorine or other treatments.
Products to Correct pH
pH Minus (pH Reducer)
Common compositions:
| Product | pH | Form | Notes |
|---|---|---|---|
| Sodium bisulphate | 1.2 | Granular | Safer, most common |
| Hydrochloric acid | <1 | Liquid | Stronger, more dangerous |
| Sulphuric acid | <1 | Liquid | Industrial, not recommended |
Sodium bisulphate (recommended):
- Safer to handle
- Dissolves well
- Doesn't release gases
- Available at pool shops
pH Plus (pH Increaser)
Common compositions:
| Product | pH | Form | Notes |
|---|---|---|---|
| Sodium carbonate (soda ash) | 11.5 | Granular/powder | Most common |
| Sodium bicarbonate | 8.4 | Granular | Milder effect, also increases alkalinity |
| Sodium hydroxide | 14 | Liquid | Industrial, not recommended |
Dosages for Correction
Lower pH (use pH Minus)
Sodium bisulphate to lower by 0.2 units:
| Pool Volume | Quantity |
|---|---|
| 20 m³ | 150-200g |
| 40 m³ | 300-400g |
| 60 m³ | 450-600g |
| 80 m³ | 600-800g |
| 100 m³ | 750-1000g |
Raise pH (use pH Plus)
Sodium carbonate to raise by 0.2 units:
| Pool Volume | Quantity |
|---|---|
| 20 m³ | 100-150g |
| 40 m³ | 200-300g |
| 60 m³ | 300-450g |
| 80 m³ | 400-600g |
| 100 m³ | 500-750g |
Dosing Rules
| Rule | Reason |
|---|---|
| Never add more than 300g/10m³ at once | Avoids sudden swings |
| Wait minimum 4 hours between additions | Time to stabilise |
| Test before adding more | Confirm effect |
| Filtration running | Even distribution |
How to Add Products
Correct Procedure
1. Preparation:
- Calculate required dose
- Use protective equipment (gloves, goggles)
- Have pump running
2. Addition method (granular):
| Method | When to Use |
|---|---|
| Dilute in bucket and distribute | Recommended |
| Add directly | Small quantities |
| Through skimmer | Never for acids |
3. Detailed procedure:
- Fill a bucket with pool water
- Add product to bucket (never the reverse!)
- Stir until dissolved
- Distribute around perimeter
- Let circulate 4-6 hours
- Test again
For Hydrochloric Acid (if using)
- Always dilute: 1 part acid to 10 parts water
- Add acid to water, NEVER water to acid
- Use in well-ventilated area
- Protective equipment mandatory
- Distribute away from metal equipment
💡 Dica Profissional
If you need a large correction (more than 0.5 units), do it in several stages over 24-48 hours. Sudden corrections can damage equipment and finishes.
Total Alkalinity (TA)
Relationship with pH
Total alkalinity (TA) acts as a pH "buffer":
| TA | pH Behaviour |
|---|---|
| Low (< 80 ppm) | Unstable pH, fluctuates a lot |
| Ideal (80-120 ppm) | Stable pH |
| High (> 150 ppm) | pH difficult to lower |
Check Before Correcting pH
Correct sequence:
- Test TA first
- If TA is low, correct before adjusting pH
- Then correct pH
Correct Alkalinity
Increase TA (sodium bicarbonate):
| To increase by 10 ppm | Quantity/m³ |
|---|---|
| Sodium bicarbonate | 15g |
Lower TA:
- Use pH Minus
- Lowers TA and pH simultaneously
- May need to raise just pH afterwards
Common Problems
pH Always Rising
| Cause | Solution |
|---|---|
| Using hypochlorite | Switch to stabilised chlorine |
| Waterfall/jets | Reduce aeration |
| Alkaline new water | Correct during filling |
| Alkalinity too high | Lower TA |
pH Always Dropping
| Cause | Solution |
|---|---|
| Too much trichlor | Use fewer tablets |
| Frequent rain | Cover pool |
| Many swimmers | Increase treatment |
| Alkalinity too low | Increase TA |
pH Won't Stabilise
| Cause | Solution |
|---|---|
| Alkalinity unbalanced | Correct TA first |
| Incorrect tests | Check kit/method |
| Wrong product addition | Review procedures |
| Problematic water source | Analyse source water |
pH Correct but Water Cloudy
| Cause | Solution |
|---|---|
| Insufficient chlorine | Increase chlorine |
| Alkalinity too high | Lower TA |
| Hardness too high | Treat limescale |
| Insufficient filtration | Increase hours |
Automatic Equipment
pH Dosers
| Type | Description | Cost |
|---|---|---|
| Manual | Basic dosing pump | ££ |
| Semi-automatic | Pump + meter | £££ |
| Automatic | Probe + pump + controller | ££££ |
Advantages of Automation
| Advantage | Description |
|---|---|
| Consistency | pH always controlled |
| Economy | Uses only what's needed |
| Comfort | Less manual work |
| Efficiency | Chlorine works better |
Probe Maintenance
| Task | Frequency |
|---|---|
| Calibration | Monthly |
| Cleaning | Weekly |
| Verification | Daily |
| Replacement | 1-2 years |
Special Situations
Well Water
In Margem Sul, especially in Palmela, Moita and rural areas of Setúbal:
| Characteristic | Action |
|---|---|
| Generally high pH | Stock pH Minus |
| Rich in minerals | Monitor limescale |
| Variable | Test more frequently |
| May have iron | Check colour |
After Heavy Rain
| Action | When |
|---|---|
| Test pH | Immediately |
| Test chlorine | Immediately |
| Correct pH | If needed |
| Shock treatment | If chlorine very low |
Filling the Pool
| Phase | Action |
|---|---|
| Before filling | Know source water pH |
| During filling | Add product gradually |
| After filling | Test and adjust |
| Before use | Confirm all parameters |
Salt Water (salt chlorination)
| Particularity | Care |
|---|---|
| Tendency for pH to rise | More pH Minus needed |
| Electrolysis releases alkaline chlorine | Monitor more frequently |
| Salt can affect readings | Use suitable kits |
pH Maintenance Checklist
Daily (intensive use)
- [ ] Check water appearance
- [ ] Test pH
- [ ] Record result
- [ ] Correct if needed
Weekly
- [ ] Test pH (minimum 2x)
- [ ] Test alkalinity
- [ ] Check product stock
- [ ] Compare with previous week
Monthly
- [ ] Complete analysis (pH, TA, hardness, chlorine)
- [ ] Check test kit (expiry)
- [ ] Clean test equipment
- [ ] Calibrate probe (if applicable)
Frequently Asked Questions
Can I swim with unbalanced pH?
With pH slightly off (7.0-7.2 or 7.6-8.0), you can swim but there will be some discomfort. With pH very off (< 7.0 or > 8.0), it's not recommended - can cause significant irritation.
Why does pH rise even without using the pool?
Carbon dioxide dissolved in water escapes naturally, especially with aeration or high temperature. This increases pH. It's completely normal.
Should I correct pH or chlorine first?
Always pH first. Chlorine only works efficiently with correct pH. Adding chlorine with high pH is wasting product.
What's the difference between sodium carbonate and bicarbonate?
Carbonate (soda ash) raises pH more. Bicarbonate raises pH little but raises alkalinity a lot. Use according to what you need to correct.
Can I use household cleaning products to correct pH?
Not recommended. Bleach (hypochlorite) has high pH but also adds chlorine. Vinegar is acidic but in very large quantities. Use proper pool products - they're safer and more effective.
Conclusion
pH control is fundamental for a healthy and comfortable pool. The essential points are:
- Keep pH between 7.2-7.6 - this is the ideal range
- Test regularly - minimum 2-3 times per week
- Correct in small doses - avoid sudden swings
- Check alkalinity first - it's the foundation of pH stability
- Wait and retest - confirm effect before adding more
- Use proper products - bisulphate to lower, carbonate to raise
Balanced pH means more efficient chlorine, more comfortable swimmers, and longer-lasting equipment.
If you need professional help with your pool's chemical balance in Margem Sul, ManutençãoPiscinas is here to help. Contact us for a no-obligation quote.
