Green water, damaged liner: the hidden cost of getting pH and chlorine wrong

When people talk about pool maintenance, the first fear is usually green water. An algae bloom is unpleasant to look at and puts a stop to swimming — but it is only the tip of the iceberg.

Repeatedly getting your chemicals wrong (pH, chlorine, stabiliser) can have far heavier financial consequences, up to the early destruction of your most expensive equipment.

📉 The domino effect: total alkalinity, pH and chlorine

To understand how the damage happens, you have to look at the water chemistry. Everything rests on a fragile balance, often summed up by the Taylor balance.

1. Total alkalinity (TA): this is your water's buffering power. If it is too low, your pH will yo-yo.
2. pH: the acidity indicator. The ideal level sits between 7.0 and 7.4.
3. Chlorine: its effectiveness depends directly on the pH. At a pH of 7.0, chlorine is roughly 75% effective. At a pH of 7.8, effectiveness falls below 30%.

If your pH is too high, you can add all the chlorine you like — it will do nothing. The water will turn green. And if you compensate by adding chlorine (and stabiliser) in bulk, you risk over-stabilisation, which blocks chlorine action for good.

💸 The real price of poor maintenance

1. A damaged liner (estimated cost: €5,000 to €15,000)

The liner is the membrane that keeps your pool watertight. It is one of the most expensive parts of the installation.

• pH too low (acidic), below 7.0: the water turns aggressive. It attacks the liner, which slackens, forms creases that never come out and loses its suppleness.
• Excess chlorine, or tablets dropped on the bottom: an overdose of chlorine, or direct contact with an undissolved tablet, causes permanent discolouration (white patches) and burns the surface, halving its lifespan.

Instead of lasting 10 to 15 years, a mistreated liner will need replacing within 5.

2. Corroded equipment (estimated cost: €500 to €2,000)

Acidic water (low pH) attacks every metal part in contact with it:

• The filtration pump shaft.
• The titanium exchanger in the heat pump.
• The shaft of a submerged roller cover.
• The ladder and the screws on the lights, which rust over.

3. Scaling (estimated cost: €200 to €1,000)

Conversely, if the pH is constantly too high (above 7.6) and the water very hard, limescale precipitates.

• The sand filter clogs and sets solid, and then has to be replaced.
• Temperature probes and electrodes — on a salt chlorinator, for instance — scale up and either give false readings or break.
• The surface turns rough, which gives algae something to cling to.

4. The forced drain-down (estimated cost: €150 to €400)

The beginner's mistake is excessive use of stabilised shock chlorine. Stabiliser (cyanuric acid) does not evaporate. Once its concentration passes 75 mg/L, the water is "locked". The only fix? Drain 30% to 50% of the pool and refill with fresh water. With the price of water rising — often more than €4 per cubic metre — and summer restrictions getting stricter every year, draining a pool has become a costly penalty and an environmental problem.

🛡️ How to avoid the worst

Problems that cost thousands of euros do not appear overnight. They are the result of weeks or months of drifting water parameters.

The answer is continuous monitoring. Hold a strict pH — 7.2, say — and an adequate disinfectant level without overdosing, and your liner, pump and filter will age in the best possible conditions.

This is where PoolNexus comes in. Instead of testing your water once a week, sometimes too late, our system analyses it around the clock. If your pH starts falling dangerously, or the chlorine level collapses, you get an immediate alert on your phone — before the water turns or the equipment suffers.

Conclusion

Do not let a saving of a few minutes' attention per week turn into a bill of several thousand euros by the end of the season. Water balance is not only about a pleasant swim: it is your pool's life insurance.