Pool Water Irritating Eyes: Incorrect pH

Introduction

Leaving the pool with red, burning eyes is an unpleasant experience that many swimmers know well. The first reaction is usually to blame the chlorine – after all, we all associate burning eyes with treated pools. However, the truth is surprising: in most cases, it's not the chlorine that's to blame, but rather the incorrect pH of the water.

pH is a measure of the acidity or alkalinity of water, on a scale of 0 to 14. Our eyes have a natural pH of approximately 7.4, and when we swim in water with a significantly different pH, we feel irritation. This is why even pools with perfectly normal chlorine levels can cause discomfort.

In Margem Sul, where the summer heat invites long swims, this problem affects many families and users of condominium pools. In this article, we'll explain in detail why pool water irritates the eyes, how to diagnose the problem, and the practical solutions to ensure comfortable swimming.

Understanding pH and Eyes

What Is pH?

pH measures the concentration of hydrogen ions in a solution:

The scale is logarithmic, meaning each unit represents a 10-fold difference. Water with pH 6 is 10 times more acidic than water with pH 7.

The Natural pH of Eyes

Our eyes have a pH of approximately 7.4, slightly alkaline. The tear film that protects the eyes maintains this stable pH. When we swim in water with different pH:

• Very low pH (< 7.0): Acidic water causes immediate irritation, intense redness, and burning sensation
• Very high pH (> 7.8): Alkaline water causes discomfort, dry eyes, and temporary blurred vision
• Ideal pH (7.2-7.6): Close to the pH of eyes, minimises irritation

Causes of Incorrect pH

Low pH (Acidic Water)

When pH is below 7.2:

Common causes:

• Excess stabilised chlorine (trichlor)
• Accumulated rainwater
• Excessive use of pH reducer
• Acid contamination
• High frequency of use without correction

Symptoms in the pool:

• Corrosion of metal equipment
• Deterioration of grout between tiles
• Chlorine very active but short-lasting
• Intense eye irritation

High pH (Alkaline Water)

When pH is above 7.6:

Common causes:

• Naturally alkaline supply water
• Excessive use of sodium hypochlorite (bleach)
• Excessive use of pH increaser
• Well water with high limestone content
• Evaporation concentrating minerals

Symptoms in the pool:

• Cloudy or milky water
• Formation of limescale deposits
• Less effective chlorine
• Dry and uncomfortable eyes

Specific Factors in Margem Sul

In our region, some factors particularly affect pH:

• Well water in Montijo, Moita, Alcochete: Generally alkaline, tends to raise pH
• Proximity to sea in Costa da Caparica, Aroeira: Sea spray can affect chemical balance
• Hot summers: High evaporation concentrates minerals and alters pH
• Condominium pools: Many users, harder to maintain balance

The Role of Chlorine in Eye Irritation

Free Chlorine vs Chloramines

Although pH is often the main culprit, chlorine can also cause irritation, especially when it forms chloramines:

Chloramines form when chlorine reacts with sweat, urine, and other organic contaminants. These are what cause the "pool smell" and much of the irritation attributed to chlorine.

The pH-Chlorine Interaction

pH directly affects chlorine effectiveness:

• pH 7.0: ~73% of chlorine is active (hypochlorous acid)
• pH 7.2: ~66% of chlorine is active
• pH 7.6: ~50% of chlorine is active
• pH 8.0: ~22% of chlorine is active

With high pH, you need more chlorine for the same disinfecting effect, increasing the risk of irritation.

Diagnosis: Why Do Eyes Burn?

Basic pH Test

Use a reliable test kit to measure:

Identifying the Cause

If pH is low (< 7.2):

• Eyes burn intensely, with redness
• Skin may feel slightly "stinging"
• Metals show signs of corrosion

If pH is high (> 7.6):

• Eyes become dry and uncomfortable
• There may be temporary blurred vision
• Water may appear cloudy

If combined chlorine is high (> 0.5 ppm):

• Strong "pool" smell
• Irritation even with correct pH
• Other swimmers also complain

When the Problem Isn't Chemical

Sometimes irritation has other causes:

• Individual sensitivity: Some people are naturally more sensitive
• Contact lens use: Increases sensitivity to water chemistry
• Already irritated eyes: Pre-existing conjunctivitis or dry eyes
• Extended time in water: Even balanced water can irritate after hours

How to Correct pH

Materials Needed

To adjust pH, you'll need:

• pH test kit (drops or strips)
• pH reducer (dry acid or liquid) – to lower
• pH increaser (sodium carbonate) – to raise
• Bucket for pre-dissolving products

Lowering pH (If It's High)

Products:

• Dry acid (sodium bisulphate) – safer
• Muriatic acid (hydrochloric acid) – stronger, more dangerous

Approximate dosage (per 10m³ of water):

Procedure:

1. Test pH and alkalinity
2. Calculate required dose
3. Pre-dissolve product in a bucket of pool water
4. Add to pool with pump running
5. Distribute evenly, avoiding concentrated areas
6. Wait 4-6 hours and test again
7. Repeat if necessary, adjusting in small increments

Raising pH (If It's Low)

Products:

• Sodium carbonate (soda ash) – raises pH and alkalinity
• Sodium bicarbonate – mainly raises alkalinity

Approximate dosage (per 10m³ of water):

Procedure:

1. Test pH and alkalinity
2. Calculate required dose
3. Pre-dissolve product in warm water
4. Add to pool with pump running
5. Wait 4-6 hours and test again
6. Repeat if necessary

The Importance of Total Alkalinity

Total alkalinity (TA) works as a "buffer" that stabilises pH:

• Low TA (< 80 ppm): pH fluctuates greatly, difficult to keep stable
• High TA (> 120 ppm): pH tends to rise and is difficult to lower
• Ideal TA (80-120 ppm): pH remains stable

Always correct alkalinity before adjusting pH for longer-lasting results.

Preventing Eye Irritation

Maintenance Routine

To avoid irritation problems:

Daily:

• Visually check water (clarity, colour)
• Remove surface debris

2-3 times per week:

• Test pH and free chlorine
• Adjust as needed

Weekly:

• Test total alkalinity
• Check combined chlorine
• Do preventive shock if needed

Monthly:

• Test all parameters
• Check equipment
• Clean filter if needed

Good Practices for Swimmers

Reduce irritation with these practices:

• Shower before entering: Removes sweat, cosmetics, and contaminants
• Wear swimming goggles: Protects eyes from direct contact
• Don't swim with eyes open for long periods: Minimise exposure
• Wash eyes after swimming: With clean water or saline solution
• Don't urinate in the pool: Contributes to chloramine formation

For Condominium Pools

In shared pools:

• Implement clear hygiene rules
• Test water more frequently
• Consider automatic pH dosing
• Do more frequent shocks in summer
• Hire regular professional maintenance

Advanced Solutions

Automatic Dosing Systems

For those who want to keep pH stable without effort:

pH dosing pumps:

• Continuously measure pH
• Add acid or base automatically
• Keep pH in ideal range
• Investment: €300-800

Advantages:

• Always stable pH
• Less eye irritation
• More effective chlorine
• Lower product consumption in the long term

Alternative Treatment Systems

Some alternatives can reduce irritation:

Salt electrolysis:

• Produces gentler chlorine
• More comfortable water for eyes
• Requires pH monitoring (tends to rise)

UV systems:

• Reduce need for chlorine
• Fewer chemicals, less irritation
• Complement traditional treatment

Ozone:

• Powerful oxidiser
• Reduces needed chemicals
• More common in commercial pools

Special Cases

Saltwater Pools

Salt electrolysis pools have their own characteristics:

• pH tends to rise naturally (from electrolysis)
• Require more frequent pH correction
• Water is generally gentler on eyes
• Salt at 3-5 g/L is similar to tears (9 g/L)

Indoor Pools

In indoor pools:

• Evaporation is lower, pH more stable
• Chloramines accumulate (less ventilation)
• Irritation may be more from chloramines than pH
• Adequate ventilation is essential

Children and Sensitive People

For more sensitive users:

• Keep pH strictly between 7.2-7.4
• Always use swimming goggles
• Limit time in water
• Wash eyes after swimming
• Consider gentler treatment systems

Costs and Products

pH Correction Products

Investment in Automation

Frequently Asked Questions

Do eyes always burn because of chlorine?

No. In most cases, the cause is incorrect pH, not chlorine. pH outside the 7.2-7.6 range irritates eyes even with normal chlorine levels. Correct pH first before changing chlorine.

What is the ideal pH to not irritate eyes?

The ideal pH is between 7.2 and 7.6, with 7.4 being the optimal value (equal to the natural pH of eyes). Within this range, most people don't feel irritation.

Why do my eyes burn even with correct pH?

If pH is correct but eyes still burn, check combined chlorine. Values above 0.5 ppm indicate presence of irritating chloramines. Do a shock treatment to eliminate chloramines.

Can I swim right after adjusting pH?

It's recommended to wait at least 4 hours after adjusting pH, or until the pump has circulated the water completely. Test again before swimming to confirm pH is in the ideal range.

Do swimming goggles solve the problem?

Swimming goggles protect eyes from direct contact with water, being a good temporary solution. However, they don't solve the underlying problem. It's preferable to correct pH so all swimmers can swim comfortably.

Conclusion

Eye irritation after swimming is often attributed to chlorine, but the real culprit is usually incorrect water pH. Key points for solving and preventing this problem are:

• Keep pH between 7.2-7.6 – close to the natural pH of eyes (7.4)
• Test regularly – at least 2-3 times per week
• Correct alkalinity first – to stabilise pH
• Check chloramines – if eyes burn with correct pH
• Use swimming goggles – as additional protection

If you need professional help with your pool in Margem Sul, ManutençãoPiscinas is here to help. Contact us for a no-obligation quote.