Pool water testing: ideal levels and how to test

Test weekly for four things: free chlorine (aim for 2 to 3 ppm), pH (7.2 to 7.6), total alkalinity (100 to 200 ppm, 120 ideal), and salt if you have a chlorinator. Strips do it in about thirty seconds; a drop-test kit is slower and reads closer. When your readings and the water disagree, take a sample to Bunnings or Mitre 10 for a store test.

What should my pool water levels be?

Keep pH between 7.2 and 7.6 and free chlorine between 2 and 3 ppm; those two decide whether the water is safe and comfortable. Then hold total alkalinity at 100 to 200 ppm so the pH stays put, and check calcium hardness and stabiliser every month or so. The ranges below are pool-equipment maker Zodiac's, checked 31 October 2026.

ppm means parts per million, the same as milligrams per litre on most kits. If your kit reads total chlorine rather than free chlorine, it is not telling you the number that matters: free chlorine is what is still available to sanitise.

What do the four pool water readings mean?

Sanitiser tells you whether anything is killing what lands in the water; pH tells you how acidic or alkaline it is, which affects how well the sanitiser works and how the water feels; total alkalinity is the water's resistance to pH swinging; and salt, on a salt pool, is the raw material the chlorinator converts to chlorine.

• Sanitiser (free chlorine, or the equivalent for your system): whether anything in the water is actually killing what lands in it. This is the one that moves fastest in hot weather and after a busy afternoon.
• pH: how acidic or alkaline the water is. It affects both how well the sanitiser works and how the water feels on skin and eyes.
• Total alkalinity: the water's resistance to pH swinging. When alkalinity is wrong, pH will not hold still no matter what you add.
• Salt: on a salt pool, the raw material the chlorinator converts to chlorine. Salt is not consumed by chlorination, but it leaves with backwashing, splash-out and overflow.

How do I test pool water at home?

1. Take the sample at elbow depth, about half a metre down, away from the return jets and the skimmer.
2. For a strip, dip it once, hold it flat for the time on the tub, and read every pad against the chart in daylight.
3. For a drop kit, fill the vial to the line, add reagent drop by drop and count until the colour turns.
4. Write the readings down with the date. A trend over a few weeks tells you far more than one reading.
5. Fix alkalinity first, then pH, then chlorine, following the label on the product you use.

Are test strips or a drop-test kit better?

Strips for routine weekly checks, a drop-test kit for working out why something is wrong. Strips read colour pads against a printed chart in about 30 seconds and go off once opened, so check the expiry. A drop kit takes a few minutes, counts reagent drops until the colour turns, and is less affected by a faded chart.

How do I test a salt water pool?

A salt pool is still a chlorine pool, so test free chlorine, pH and alkalinity exactly as above, then add a salt reading. Salt strips or a digital salt meter read it; many chlorinators also show a low-salt light. Keep salt inside the range printed on your chlorinator, because the cell is built for it.

Salt only leaves with water: backwashing, splash-out and overflow after heavy rain. So check it monthly and after any big top-up rather than weekly. pH tends to creep upward on salt pools, which is why the weekly pH check matters most on them.

Where can I get my pool water tested for free in NZ?

Bunnings New Zealand offers free in-store pool water testing: you take a sample to your nearest Bunnings Warehouse, enter a few details at the testing kiosk and get an instant summary of your water chemistry. Mitre 10 MEGA and participating Mitre 10 stores test a sample digitally. Independent pool shops often test too; ask yours.

How do I take a water sample for a shop test?

Use a clean bottle rinsed in pool water, fill it at about half a metre deep away from the return fittings, fill it to overflowing and cap it with no air gap, then get it to the store within about an hour, out of the sun. Wait 2 days after a shock dose. These are Mitre 10's own instructions.

Take your pool's volume with you, because the dose a store recommends depends on it. Mitre 10's rule is length × width × average depth in metres × 1,000 = litres; our pool volume guide works it through for round and freeform pools.

How often should I test my pool water?

At least once a week in the swimming season, and more often after heavy rain or a lot of swimmers, which is Zodiac's advice. Calcium hardness and stabiliser move slowly, so monthly is enough for those. Through a New Zealand winter, with the pool covered and little use, many owners drop to every week or two.

How much chlorine should I add?

That depends on the product's strength and your pool's real volume, so follow the label on the product you own rather than a generic table. Work out your volume properly (our pool volume guide shows how), and when you are unsure, a store water test gives you a dose for your pool and that product.

Running a pool costs more than chemicals: power, heating and the three-yearly fence inspection all add up. Our pool running costs guide puts them in one place, and the pool care pages cover the kit.