Understanding Water Chemistry

You don't need to be a chemist to understand your pool water — but knowing the basics helps you make sense of your service reports and know when something needs attention.

Why water chemistry matters

Balanced pool water does three things:

• Keeps swimmers safe — properly sanitised water prevents bacteria and algae from growing.
• Protects your pool and equipment — water that's too acidic or too soft will corrode fittings, damage the pool shell, and shorten the life of your pump and filter.
• Makes your pool look good — balanced water is clear and inviting. Unbalanced water goes cloudy or green.

Chlorine — your pool's sanitiser

Chlorine is what keeps your pool clean and safe to swim in. It kills bacteria, viruses, and algae. The level needs to stay in range — too low and the pool isn't being sanitised, too high and it can irritate skin and eyes.

NZ and AU summers are tough on chlorine — high UV levels, warm temperatures, and heavy bather loads all use it up faster. Your technician adjusts chlorine at every visit.

pH — the balance dial

pH measures how acidic or alkaline your water is. The ideal range is 7.2–7.6. Think of it like a dial:

• Too low (acidic) — water irritates eyes and skin, corrodes metal fittings, and can damage the pool surface.
• Too high (alkaline) — chlorine becomes much less effective, water goes cloudy, and scale builds up on surfaces and the waterline.

pH is one of the readings your technician will adjust most often.

Alkalinity — the stabiliser for pH

Total alkalinity is best thought of as a buffer for your pH. When alkalinity is in range (80–120 ppm), pH stays stable and is easy to adjust. When alkalinity is too low, pH bounces around and becomes hard to control. When it's too high, pH gets "locked" in one place and won't respond well to treatment.

Stabiliser — protecting chlorine from the sun

Cyanuric acid (also called stabiliser or conditioner) slows down how quickly UV light destroys chlorine. Without it, chlorine added to your pool on a sunny New Zealand day can disappear within hours.

The ideal range is 30–50 ppm. Too much stabiliser can actually make chlorine less effective — a problem known as chlorine lock. Stabiliser levels only go down when you dilute the pool with fresh water, so they tend to creep up over time.

What flagged readings mean

In your service report, a reading shown in red means it was outside the safe range when your technician visited. Your pool company is aware — the reading is flagged in their system and your technician will address it.

In most cases, your technician will have already treated the issue during the visit. If the situation is urgent, they or your pool company will contact you directly. You don't need to take any action unless they've asked you to.

Questions about your readings?

If you see a red reading in a report and want to understand what it means or what was done, you can message your pool company via the Request tab or call them directly.