The “ideal” pool chlorine level isn’t what’s on the back of your test kit
Every pool test kit and every chlorine bottle in Australia says “1–3 ppm”. That target is correct only for a pool with zero cyanuric acid. For every other pool, meaning every outdoor pool, the right target is higher. Here’s the math.
Last updated: 2 June 2026
The chlorine level printed on the back of every test kit in Australia says 1–3 ppm. The chlorine level recommended on the back of every chlorine product says 1–3 ppm. The chlorine level your local pool shop tells you to maintain is 1–3 ppm.
That target is correct for one specific case: a pool with zero cyanuric acid. For an indoor pool, that means most of the time. For an outdoor pool, meaning every pool that’s used a stabilised chlorine product or had any CYA added, that target is wrong. And not by a small amount.
This guide explains the actual relationship between cyanuric acid and the chlorine level your pool needs. The full chemistry behind it is in our chlorine lock guide; this page is the practical “what should my chlorine reading be” reference.
The CYA-adjusted free chlorine table
This is the table to keep on your phone:
| CYA (ppm) | Minimum FC (ppm) | Target FC (ppm) | Shock FC (ppm) |
|---|---|---|---|
| 0 | 0.5 | 1–3 | 10 |
| 20 | 1.5 | 2–4 | 10 |
| 30 | 2 | 3–5 | 12 |
| 40 | 3 | 4–6 | 16 |
| 50 | 4 | 4–7 | 20 |
| 60 | 5 | 5–8 | 24 |
| 70 | 5.5 | 6–9 | 28 |
| 80 | 6 | 6–11 | 31 |
| 90 | 7 | 7–12 | 35 |
| 100 | 8 | 7–13 | 39 |
| 110 | 9 | 8–14 | 43 |
| 120 | 10 | 9–15 | 47 |
| 150 | 12 | 11–17 | 59 |
The formulas behind the table:
- Minimum FC = CYA × 0.075 (7.5%)
- Target FC = CYA × 0.115 (11.5%)
- Shock FC = CYA × 0.40 (40%)
The minimum and target come from the Trouble Free Pool community’s analysis of the Pickens method (Richard Falk’s research) on the chlorine/CYA relationship. The shock level is the break-point chlorination threshold adjusted for CYA buffering.
What the table actually means in practice
Reading example 1: New pool, no CYA added yet
CYA = 0 ppm. Target FC = 1–3 ppm. The classic “1–3 ppm” target is correct here. Easy to maintain because UV doesn’t burn off chlorine until you add some CYA, but you need to top up chlorine multiple times a day during midday sun.
Reading example 2: Outdoor chlorine pool with CYA at 50 ppm
This is the most common Australian residential scenario. Target FC = 4–7 ppm, not 1–3. If you’ve been maintaining “1–3 ppm” here, your pool is regularly below the minimum sanitiser threshold, and you’ll have algae blooms 2–3 times a season.
Reading example 3: Saltwater pool with CYA at 70 ppm
Saltwater pools typically run higher CYA. Target FC = 6–9 ppm. The salt cell needs to produce enough chlorine to maintain this level, which means appropriate cell sizing and run time. Many “low chlorine on saltwater pool” complaints are CYA-induced.
Reading example 4: Pool with CYA at 120 ppm (chlorine lock zone)
You’re in chlorine lock territory. Target FC = 9–15 ppm. Maintaining this level is impractical without continuous heavy chlorination. The right fix isn’t to maintain that FC; it’s to drain and refill to bring CYA back to 50 ppm. See our chlorine lock guide.
Why “1–3 ppm” became the universal default
The 1–3 ppm target dates from before stabilised chlorine products became widespread (pre-1980s). At that time, most outdoor pools didn’t have CYA in them, so the static target was correct. The figure stuck in industry literature, on test kit labels, and on chemical product packaging, even as the actual chemistry of typical outdoor pools changed.
The result: 40+ years of pool owners following advice that was correct in 1965 and wrong now. Most don’t realise this. Many pool service technicians don’t realise this. Even some pool stores don’t.
The shortcut: if your CYA reading is between 30 and 80 ppm, multiply your CYA by 0.115. That number is your target FC. If your actual FC is below CYA × 0.075, you’re below the algae-prevention threshold even if your test strip says “looks fine”.
Free chlorine targets by pool type
| Pool type | Typical CYA | Target FC |
|---|---|---|
| Indoor chlorine pool (no CYA) | 0 ppm | 1–3 ppm |
| Outdoor chlorine pool | 30–50 ppm | 3–7 ppm |
| Outdoor saltwater pool | 60–80 ppm | 5–11 ppm |
| Spa / hot tub (chlorine) | 0–30 ppm | 3–5 ppm |
| Spa / hot tub (bromine) | n/a | 3–5 ppm bromine |
| Public swimming pool | 30–50 ppm | 2–4 ppm (regulation minimum) |
| Heated pool (summer use) | 30–50 ppm | 5–7 ppm (extra demand from warm water) |
Combined chlorine, the parameter that signals trouble
Free chlorine (FC) is what’s available to sanitise. Combined chlorine (CC) is what’s already reacted with organic matter, chloramines. Total chlorine (TC) = FC + CC.
Combined chlorine should be below 0.5 ppm at all times. Anything higher means:
- Sanitiser demand is outrunning supply
- Chloramines are building up in the water
- That “pool smell” and eye-sting is going to start
- You’re approaching algae bloom territory
If CC creeps above 0.5 ppm, shock the pool (target FC = 10 × CC) to break the chloramines. Don’t wait for visible problems.
How to maintain target FC reliably
For a chlorine pool with liquid chlorine
For a 50,000 L pool with target FC of 6 ppm, daily summer chlorine demand is typically 2–4 ppm (UV loss + sanitisation demand). That’s 800–1600 mL of 12.5% liquid chlorine per day. Add in the evening when UV is gone.
For a chlorine pool with cal-hypo
Roughly 200 g of 65% cal-hypo per 50,000 L raises FC by 4 ppm. Add once daily, in evening.
For a chlorine pool with trichlor tabs
Trichlor dissolves at roughly 250–500 g per day from a floating dispenser, depending on flow. Convenient, but adds CYA. After a few months of trichlor use, your CYA will be high enough to need a different chlorine source.
For a saltwater pool
Set cell output to match daily demand. Typical Australian summer setting is 60–80% output on a properly-sized cell. If cell needs to run 100% to maintain FC, either cell is undersized or CYA is too low (causing excess UV loss).
Sources & references
- Trouble Free Pool, ABCs of Pool Water Chemistry
- Richard Falk, The Chlorine/CYA Relationship
- ANSI/APSP-11, Water Quality Standards in Public Pools
- AS 3633-1989, Private swimming pools (Australian Standard)
- CDC Healthy Swimming guidance
Frequently asked questions
What is the ideal free chlorine level for a pool?
It depends on your cyanuric acid (CYA) level, there’s no single ‘ideal’ number for all pools. The target is CYA × 0.115, with a minimum of CYA × 0.075. For an outdoor chlorine pool at CYA 50 ppm, target FC is 4–7 ppm, not the generic ‘1–3 ppm’ on test kit charts.
Is 5 ppm chlorine too high for swimming?
No. The WHO and CDC consider FC up to 10 ppm safe for swimming. The ‘don’t swim above 4 ppm’ rule comes from an outdated era when CYA wasn’t widespread. With CYA at 50+ ppm, FC of 5–7 ppm is normal and safe.
Why is my chlorine reading high but the pool is still going green?
Most likely your CYA is too high (above 80 ppm). At high CYA, your measured free chlorine is artificially high, only a small percentage of it is in the active sanitising form. Test CYA and recalculate your target as 11.5% of your reading.
Should saltwater pools have higher chlorine than chlorine pools?
Saltwater pools typically maintain higher FC (5–8 ppm) because they also typically have higher CYA (60–80 ppm). The CYA × 0.115 formula applies to all chlorine-sanitised pools, saltwater is just a different chlorine delivery method, same chemistry.
Can I have too much chlorine in my pool?
Yes, above ~10 ppm FC with low CYA, swimmers can experience eye and skin irritation. With high CYA (80+ ppm), even 15 ppm FC is comfortable because most is bound to CYA. The ‘too much chlorine’ threshold scales with CYA, not a fixed number.
Will the Water Test Calculator app calculate the right chlorine target?
Yes. The app applies the CYA-adjusted target automatically, you enter your CYA reading and the target FC is calculated as 11.5% of CYA. No looking up charts, no manual math. Launching on iOS and Android in approximately 10 days.
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