Pool pH: What It Should Be, and How to Keep It Steady

If you could only test one thing in your pool, test pH. Not because it matters more than chlorine, but because pH decides whether the chlorine you add is able to work at all.

Plenty of pool owners dose chlorine exactly by the book and still have cloudy water and algae. Then they test pH and find it has drifted up to 8.2, the point at which chlorine has largely given up.

The target is 7.2-7.6

This range is the balance point: chlorine still sanitises well, and the water is kind to both swimmers and the pool itself.

Below 7.2 the water turns acidic and starts eating render, grout and metal parts in the filtration system. Swimmers get stinging eyes and dry skin.

Above 7.6 chlorine loses strength progressively, water starts to cloud, scale forms on the walls, and swimmers get sore eyes anyway.

One common misunderstanding worth clearing up: stinging eyes does not necessarily mean too much chlorine. Far more often it is a pH problem.

How and how often to test

A home pool should be tested at least once a week, and more often during heavy use or heavy rain.

The simplest option is a liquid test kit, which reads chlorine and pH together. It is inexpensive and refill reagent is sold separately.

For something faster, Insta-TEST 5 Plus strips give six readings from one dip. For a precise number, there are digital meters with replaceable probe tips.

Down with pH Minus, up with pH Plus

If the reading is high use pH Minus. If it is low use pH Plus. These two are our best-selling products, for the simple reason that every pool needs them regularly.

Three rules when dosing.

One: add in portions. Do not tip in the whole pail hoping to land on the number. Overshooting and correcting back wastes chemical twice over.

Two: dissolve before you add, and spread it around the pool with the pump running rather than dumping it in one spot.

Three: wait 4-6 hours before retesting, so the water has turned over. Only then is the reading true for the whole pool.

If pH will not stay put, the problem is alkalinity

This is the part worth knowing. If you correct pH and it bounces back within two days, no matter how much you add, the problem usually is not pH at all. It is total alkalinity.

Alkalinity acts as a buffer for pH. When it is too low, pH has nothing anchoring it and swings easily.

The right range is 80-150 ppm, raised with Alkalinity Up at 200 g per 10,000 litres for each 10 ppm.

The correct sequence is get alkalinity right first, then adjust pH. Doing it the other way round is a lot of work for nothing.

One more value worth knowing: hardness

Calcium hardness should sit at 200-500 ppm. Too low and the water starts pulling calcium out of the render and grout instead, ageing the pool without the owner noticing.

Raise it with Water Hardener. This one does not need testing as often as pH — two or three times a year is enough.

In short

Test pH weekly and hold it at 7.2-7.6. If it will not settle, look at alkalinity first. Do that and the chlorine you add every week starts earning its keep.

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