Pool Water Chemistry 101: The Complete Beginner's Guide

Key takeaway: Five numbers run every backyard pool: pH 7.2 to 7.6, total alkalinity 80 to 120 ppm, calcium hardness 200 to 400 ppm for concrete or tiled pools (100 to 250 ppm for vinyl or fibreglass), free chlorine 1 to 3 ppm, and cyanuric acid 30 to 50 ppm. Always correct alkalinity before touching pH. It’s the step most quick-reference charts skip, and the reason two dosing guides can both look “right” and still disagree by 10x.

Pool water chemistry is the set of five measurable properties, pH, total alkalinity, calcium hardness, free chlorine (or another sanitiser), and cyanuric acid, that determine whether your water is safe to swim in, comfortable on skin and eyes, and not slowly eating its own tiles, liner or equipment. Your pool turns cloudy overnight, or your eyes sting after ten minutes even though you dosed chlorine yesterday, and the cause is almost always chemistry, not cleaning. Get all five roughly right, in the right order, and the water mostly looks after itself. Get one wrong and every other symptom, algae, stinging eyes, scaling, corroded fittings, traces back to it.

This guide is the hub for everything else we cover on pool care and water chemistry. Use it to understand how the five numbers fit together, then follow the links below to the specific fix, calculation or comparison you actually need.

A note on chemical safety: liquid chlorine, pool acid and calcium hypochlorite shock are classified as hazardous, corrosive substances under SafeWork Australia and ADG Code criteria. Always add chemicals to water, never water to chemicals, store acid and chlorine products separately (they react violently if mixed), and wear gloves and eye protection when handling concentrated product. For any chemical exposure, call the Australian Poisons Information Centre on 13 11 26, available 24 hours a day from anywhere in Australia.

The Five Numbers That Run Your Pool

These are the parameters every pool test kit measures, and roughly what a backyard pool in Australia should be sitting at:

Parameter	Target range	Why it matters	Test how often
pH	7.2 to 7.6 (AS 3633’s operating range is wider: 7.0 to 7.8)	Controls how well chlorine sanitises, and how comfortable the water feels on skin and eyes	Daily, ideally before the first swim of the day
Total alkalinity	80 to 120 ppm (AS 3633 range: 60 to 200 ppm)	Buffers pH so it doesn’t swing wildly, sometimes called “pH bounce”	Weekly, or whenever pH won’t hold
Calcium hardness	200 to 400 ppm concrete or tiled; 100 to 250 ppm vinyl or fibreglass (AS 3633 range: 80 to 500 ppm)	Too low corrodes surfaces and equipment; too high causes scale build-up	About once a year, more often if you sanitise with calcium hypochlorite
Free chlorine	1 to 3 ppm	The actual sanitiser. It’s what kills bacteria and algae, not the total chlorine reading	Daily to every few days
Cyanuric acid (stabiliser)	30 to 50 ppm	Shields chlorine from being burned off by UV sunlight; too much and chlorine stops working properly (“chlorine lock”)	Monthly, or at the start of each season

Sources: pH, total alkalinity and calcium hardness ranges are Standards Australia’s AS 3633 as summarised in SPASA Victoria’s Fact Sheet 5, Water Balance; testing frequency per Better Health Channel, Swimming pools: water quality (Victorian Government). Free chlorine and cyanuric acid figures aren’t set by AS 3633 at all. They’re the range most Australian pool shops and manufacturers test to.

A quick honesty check most guides skip: Australian sources don’t fully agree on the total alkalinity “sweet spot”. AS 3633 itself only sets a wide operating band of 60 to 200 ppm. Within that, some Australian pool shops recommend 80 to 120 ppm, while SPASA Victoria’s own consumer fact sheet targets 120 to 160 ppm for swimming pools. There’s no single correct number here. What actually matters is picking a target inside the 60 to 200 ppm band and holding it steady, since it’s stability, not the exact figure, that keeps pH from swinging.

Why Order Matters: Fix Alkalinity Before pH

Total alkalinity is the reason two pool-care guides can both be technically correct and still disagree by 10x on how much acid or buffer to add for the same pH shift. Alkalinity acts as a chemical buffer. The higher it sits, the more the water resists a pH change, so a pool at 200 ppm alkalinity needs several times more acid to move pH by 0.1 than a pool sitting at 80 ppm. Correct alkalinity first, into range, and pH becomes far easier, and far more predictable, to adjust afterwards.

This is the step almost every quick-reference chart skips, and it’s the single biggest reason “I added exactly what the chart said and nothing happened” complaints show up in pool forums and Facebook groups. For the full step-by-step process, see our guide on how to raise pH in a pool, which starts with the same alkalinity check before touching acid or buffer.

How to Choose Your Sanitiser: Chlorine, Salt or Mineral

Every pool needs a sanitiser, something that continuously kills bacteria and algae, and in Australia that’s almost always one of three systems. They’re less different than the marketing suggests: a salt chlorinator still makes chlorine, it just manufactures it on-site from dissolved salt (typically 4,000 to 5,000 ppm for a standard Australian unit) instead of you pouring it in from a bottle. A mineral system adds copper or silver minerals to reduce, not eliminate, how much chlorine you still need. None of the three is genuinely “chlorine-free”, whatever the box says.

System	How it works	Trade-off	Best for
Liquid or granular chlorine	You dose chlorine by hand from a bottle or bucket	Cheapest to set up; the most hands-on ongoing effort	Renters, small pools, tight up-front budgets
Salt chlorinator	A cell electrolyses dissolved pool salt (around 4,000 to 5,000 ppm) into chlorine automatically	Higher upfront cost; lower ongoing effort and softer-feeling water	Most owner-occupied backyard pools
Mineral system	Copper or silver minerals plus a reduced, still-necessary chlorine dose	Most expensive upfront; gentlest on skin and eyes	Sensitive skin or eyes, lower top-up chlorine needs

A salt chlorinator costs more to install than a bottle of liquid chlorine, but a chlorinator cell typically lasts several years and needs far less week-to-week product, so the ongoing running cost is usually lower over the life of the equipment. The upfront-versus-ongoing trade-off matters more than any single sticker price.

What It Costs to Keep Your Pool Balanced

The biggest driver of your chemical bill isn’t brand, it’s volume. A 50,000 litre pool needs roughly double the chemicals of a 25,000 litre pool for the same correction, every single time you dose. If you don’t already know your pool’s volume in litres, that’s the first number every calculation in this guide depends on, including every product label’s “dosage per X litres” instructions. A pool volume calculator makes this quick (coming soon on this site), and once you have that number, every other calculation, salt, chlorine, acid, alkalinity, gets easier and more accurate.

Your Weekly, Monthly and Seasonal Routine

Better Health Channel‘s guidance for private pools is to check pH and chlorine daily, ideally before the first swim of the day, and to test more often in hot weather. In practice that breaks down into three rhythms:

Weekly: test pH and free chlorine (daily in the middle of summer or after heavy pool use); check total alkalinity if pH keeps drifting.
Monthly, or each season: test cyanuric acid and calcium hardness. Both change slowly, so they don’t need constant checking.
After anything unusual: heavy rain, a big pool party, or topping up with a lot of fresh water all dilute or shift your chemistry and are worth a full re-test, not just a quick chlorine check.

Spring is also when most Australian pools need their first real chemistry reset after a dormant winter: low chlorine, drifted pH, and the start of algae season all converge at once. If your pool’s gone green over winter, our guides on why your pool turns green and how to shock a pool cover the reset in full, and both assume you’ve already got a current pH and alkalinity reading before you start.

More Pool Water Chemistry Guides

This hub links down to the rest of our pool care and water chemistry library. We’re adding new guides on a rolling basis, so check back if the specific fix you need isn’t here yet:

Frequently Asked Questions

What should the pH of a pool be?

The recommended range for an Australian backyard pool is 7.2 to 7.6, sitting inside AS 3633’s wider 7.0 to 7.8 operating band. Anything much above 7.6 stops chlorine working properly and can sting skin and eyes; anything below 7.0 is acidic enough to corrode metal fittings and irritate eyes.

How accurate are pool test strips?

Test strips are accurate enough for a quick between-tests check, but a liquid reagent kit reads pH, chlorine and alkalinity more precisely and is worth using for any reading you’re about to dose against. Strips are also more sensitive to age, humidity and how long you dip them, so an old or damp strip will drift even when your water hasn’t.

What should calcium hardness be in a pool?

200 to 400 ppm for concrete or tiled pools, and 100 to 250 ppm for vinyl-liner or fibreglass pools, inside AS 3633’s overall 80 to 500 ppm range. The lower range for fibreglass and vinyl exists because these surfaces are more prone to staining from calcium build-up than concrete.

What is free chlorine in a pool?

Free chlorine is the portion of chlorine in your water that’s still active and available to sanitise, as opposed to combined chlorine, which has already reacted with contaminants and is doing nothing further. The 1 to 3 ppm target refers specifically to free chlorine, not total chlorine, which is why two pools can both read 3 ppm chlorine and one still smells strongly of chemicals while the other doesn’t.

What chemicals do I need for a saltwater pool?

A saltwater pool still needs the same five things checked, pH, alkalinity, calcium hardness, cyanuric acid and (via the chlorinator) free chlorine, plus pool salt itself, typically maintained around 4,000 to 5,000 ppm for a standard Australian chlorinator. Salt water doesn’t mean chemical-free; it means the chlorine is manufactured on-site instead of added from a bottle.

What causes algae in a pool?

Algae grows when free chlorine drops too low to keep killing it, usually from poor circulation, heavy rain diluting the water, a chlorinator that’s not keeping up in hot weather, or cyanuric acid creeping high enough to blunt the chlorine you do have. It’s very rarely one single cause; it’s chlorine losing the fight for any of several reasons at once.

How much does pool maintenance cost in Australia?

It depends mainly on your pool’s volume and sanitiser system rather than a fixed national figure. A salt chlorinator generally costs more to install but less to run week to week than manually dosed chlorine. We don’t quote a single dollar figure here because it varies too much by state, pool size and system; see our sanitiser comparison above for the trade-offs that actually drive the cost.

Salt chlorinator vs chlorine pool, which is better?

Neither is objectively better. A salt chlorinator costs more upfront and needs less week-to-week effort, while manually dosed chlorine is cheaper to start and gives you more direct control over the dose. Both systems ultimately sanitise with chlorine; the salt system just makes its own instead of you adding it from a bottle.

How often should I test my pool water?

Daily for pH and free chlorine, ideally before the first swim of the day, per Better Health Channel’s guidance for private pools, weekly to monthly for total alkalinity, and roughly once a season for calcium hardness and cyanuric acid, since those two shift far more slowly.

Can I use pool chemicals from any brand, or do I need to match my chlorinator?

Core chemicals, pool salt, acid, buffer, algaecide, aren’t brand-locked to your chlorinator; a generic product that meets the same specification works fine. The exception is anything that touches the chlorinator cell itself or its control settings, where it’s worth checking your unit’s manual before mixing brands.

What’s the first thing I should test if my pool water looks off?

Total alkalinity and pH, in that order. Together they explain the majority of cloudy-water, stinging-eyes and chlorine-won’t-hold complaints, and correcting alkalinity first makes every other fix more predictable.

Sources