How to Balance Pool Water: The Order and Saturation Check

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To balance pool water, adjust in this order: total alkalinity first (60–200 mg/L, SA Health), then pH (7.2–7.6), calcium hardness, stabiliser (30–50 mg/L) and chlorine last (1.0–3.0 mg/L free). Then check the saturation index: NSW Health’s target is −0.3 to +0.3, and the same water reads 0.0 at 29°C and −0.4 at 12°C.

The short answer

The A-P-C-S-C order: alkalinity, pH, calcium, stabiliser, chlorine. Each step changes the one after it, so fixing them out of order means fixing them twice.
Alkalinity before pH because NSW Health says low alkalinity lets pH change rapidly and high alkalinity makes pH difficult to adjust; acid and bicarb move both.
The bands (home): alkalinity 60–200 mg/L, pH 7.2–7.6, calcium 150–400 mg/L, stabiliser 30–50 mg/L, free chlorine 1.0–3.0 mg/L (SA Health). NSW Health’s saturation-index targets differ: alkalinity 60–180, calcium 200–400 for concrete, 80–200 for fibreglass.
Worked index, salt pool: pH 7.6, alkalinity 115 less 30% of 50 stabiliser = 100, calcium 200: LSI 0.0 at 29°C, −0.3 at 16°C, −0.4 at 12°C.
Balance for the coldest month: calcium at 300 mg/L keeps the same pool at −0.2 in winter and +0.2 in summer, both inside −0.3 to +0.3.

The pool water balance table, in the order to adjust: home-pool bands (SA Health, HealthyWA), public-pool limits (NSW Public Health Regulation 2022 via NSW Health’s 2026 guidelines, labelled), and the narrower targets NSW Health gives for correcting the saturation index (Appendix E); read 20 October 2026
Adjust in this order	Home pool band	Public pool limit (NSW)	NSW saturation-index target	Why it comes here
1. Total alkalinity	60–200 mg/L (SA Health)	80–200 mg/L (NSW Regulation)	60–180 mg/L	It buffers pH: too low and pH swings, too high and pH will not move (NSW Health)
2. pH	7.2–7.6 (SA Health); 7.2–7.8, 7.5 ideal (HealthyWA)	7.0–7.8 (NSW Regulation)	7.2–7.6	Sets how much of the chlorine is working; acid and alkali both move alkalinity too
3. Calcium hardness	150–400 mg/L (SA Health)	No regulated limit	200–400 masonry; 80–200 vinyl or fibreglass	Only dilution lowers it, so set it against the index once pH and alkalinity are fixed
4. Stabiliser (cyanuric acid)	30–50 mg/L (SA Health, HealthyWA)	Max 50 mg/L, outdoor pools only	Deduct 30% of it from alkalinity	Sets the chlorine minimum: NSW public outdoor pools need 3.0 mg/L free with it, 1.0 without (pH 7.6 or less)
5. Free chlorine	1.0–3.0 mg/L, ideal 2 (SA Health); stabilised pools at least 2 below 26°C, 3 above (HealthyWA)	Outdoor with cyanuric acid: min 3.0 (pH 7.6 or less), 4.0 (above 7.6)	Not in the index	Last, because the target depends on steps 2 and 4

How do I balance my pool water? Alkalinity, pH, calcium, stabiliser, chlorine

Test everything first, with one kit, on one sample: free and total chlorine, pH, total alkalinity, calcium hardness and stabiliser, plus salt in a salt pool. Then adjust one parameter at a time, in the order of the table, retesting between steps.

Total alkalinity. NSW Health’s 2026 guidelines: if total alkalinity is too low, pH can change rapidly; if it is too high, pH will be difficult to adjust. Lowering pH with acid also lowers alkalinity. Raise it with bicarb, as on how to raise alkalinity without raising pH; lower it with acid, as on how to lower alkalinity.
pH. With alkalinity steady, pH holds where you put it. How to lower pH and how to raise pH have the doses.
Calcium hardness, judged by the saturation index below rather than the number alone. How to raise pool hardness; how to lower pool hardness (dilution only).
Stabiliser, outdoor pools only, 30–50 mg/L. How to raise pool stabiliser; how to lower pool stabiliser.
Chlorine, last, to the minimum the pH and stabiliser now call for. How to raise pool chlorine; how to lower pool chlorine. In a salt pool, set salt to the chlorinator manual first: what salt level a pool should run at.

The A-P-C-S-C rule: alkalinity, pH, calcium, stabiliser, chlorine, because each step moves the one after it and none moves the one before. The order is our synthesis of what the health guidance says each chemical does; the doses are on the linked pages and this hub does not restate them.

How do I know my pool water is balanced? The saturation index, summer and winter

Each reading can be inside its band and the water still be corrosive or scale-forming. NSW Health’s 2026 guidelines use the Langelier Saturation Index: LSI = pH + temperature factor + calcium hardness factor + total alkalinity factor − TDS factor, where the TDS factor is 12.1 below 1,000 mg/L and 12.2 above (every salt pool). In a stabilised outdoor pool, deduct 30% of the cyanuric acid reading from alkalinity first. The ideal is 0 or slightly positive, within −0.3 to +0.3; negative water attacks fixtures and fittings, positive water scales.

Worked example, one salt pool through the year. pH 7.6; alkalinity reads 115 with stabiliser 50, so corrected alkalinity is 115 − 15 = 100 (factor 2.0); calcium 200 (factor 1.9); TDS factor 12.2. Temperature factors from NSW Health’s Table E-1: 29°C 0.7, 16°C 0.4, 12°C 0.3.

Season and change	pH + temp + calcium + alkalinity − TDS	LSI	Verdict
Summer, 29°C	7.6 + 0.7 + 1.9 + 2.0 − 12.2	0.0	Balanced (NSW Health ideal 0, range −0.3 to +0.3)
Autumn, 16°C	7.6 + 0.4 + 1.9 + 2.0 − 12.2	−0.3	At the corrosive edge
Winter, 12°C	7.6 + 0.3 + 1.9 + 2.0 − 12.2	−0.4	Corrosive: outside the range
Winter, 12°C, calcium raised to 300	7.6 + 0.3 + 2.1 + 2.0 − 12.2	−0.2	Inside the range
Summer, 29°C, calcium 300	7.6 + 0.7 + 2.1 + 2.0 − 12.2	+0.2	Still inside the range

The coldest-month rule: balance the index at your pool’s winter temperature, because the same water loses 0.4 between 29°C and 12°C. Raising calcium from 200 to 300 mg/L keeps this pool inside the range all year. Skip the stabiliser correction and alkalinity of 115 reads about 2.06 instead of 2.0, overstating the index by about 0.06; small, but it is the margin at the edge of the range. A different worked index, raising calcium from 100 in summer, is on how to raise pool hardness.

How to balance pool water in a fibreglass pool

Same order, lower calcium. NSW Health’s Appendix E puts calcium hardness at 80–200 mg/L for vinyl or fibreglass against 200–400 for masonry. With calcium at 150 (factor 1.8) the summer example above reads −0.1 and the winter one −0.5, so a fibreglass pool corrects a cold-water index through pH and alkalinity rather than calcium: NSW Health says pH is the more important and ideally 7.2–7.6. If the shell is already chalky or blistered, fibreglass pool problems and what to check covers the surface.

How often to rebalance, and when balancing is not enough

Chlorine and pH move daily; alkalinity, calcium and stabiliser weekly. How often pool water should be tested sets out the schedule by parameter. A pool that will not hold its balance after a correct sequence usually has a reading only dilution fixes, stabiliser above 50 mg/L, calcium above its band or dissolved solids too high; how often pool water should be changed gives the ceilings, and how often to shock a pool covers combined chlorine.

If the pool keeps scaling or etching with the index in range, the cause is the surface or the equipment; pool equipment explained sets out what to check, and you can compare pool quotes on a written scope.

Common questions

What order do you balance pool chemicals in?

Total alkalinity, pH, calcium hardness, stabiliser, then chlorine. The NSW Health 2026 pool water guidelines say low alkalinity lets pH swing and that acid lowers both, which is why alkalinity comes first.

How do I balance pH and alkalinity in my pool?

Set alkalinity first, 60–200 mg/L on SA Health’s home guidance, then adjust pH to 7.2–7.6. Acid lowers both; bicarb raises alkalinity with little pH change; soda ash raises pH quickly.

What is a balanced saturation index for a pool?

0 or slightly positive, within −0.3 to +0.3, on NSW Health’s 2026 guidelines. Negative water is corrosive; positive water forms scale.

Why does my pool go out of balance in winter?

Colder water lowers the saturation index. In our worked salt pool, the same chemistry reads 0.0 at 29°C and −0.4 at 12°C, which is corrosive.

Do I need to balance a salt water pool differently?

Same order, plus salt to the chlorinator manual. Salt pools are over 1,000 mg/L dissolved solids, so the index uses a factor of 12.2, not 12.1, reading 0.1 lower.

Sources

General information only, current at 2026-10-20. Pool rules differ by state and by council, and penalty amounts are updated regularly. Confirm your own obligations with your council or a registered inspector before acting.