Commercial Pool Chlorine Range: What Should You Use?

Under the CDC's 2024 Model Aquatic Health Code (MAHC), free chlorine must stay at or above 1.0 ppm in pools without stabilizer, 2.0 ppm in pools with stabilizer, and 3.0 ppm in spas. The top of the range comes from the chlorine product's label.

Why are the limits set on free chlorine?

Because free chlorine is the part still doing the disinfecting. CDC's chloramines guidance explains that chlorine which binds to body waste, such as sweat, forms chloramines, a type of combined chlorine. Total chlorine counts both, so it can look fine while free chlorine is low. Our guide to free chlorine vs total chlorine shows how to label each one.

What chlorine numbers does the MAHC set?

Here is what the 2024 MAHC says. It is not federal law, so check which numbers your state adopted:

Item	2024 MAHC number	Section
Free chlorine minimum, no cyanuric acid	1.0 ppm	5.7.3.1.1.2.1
Free chlorine minimum, with cyanuric acid	2.0 ppm	5.7.3.1.1.2.2
Free chlorine minimum, spas	3.0 ppm	5.7.3.1.1.2.3
Free chlorine maximum	What the product label allows	5.7.3.1.1.5
pH	7.0 to 7.8	5.7.3.4.1
Cyanuric acid maximum	90 ppm	5.7.3.1.3.2
Combined chlorine	Act to lower it above 0.4 ppm	5.7.4.4.2

When must a pool close for chlorine or pH?

The MAHC calls these imminent health hazards (6.6.3.1). The owner, operator or person in charge must close the pool for any of them (6.6.3.2), and the health department can also order it fixed or closed right away. These involve chlorine and pH:

• Free chlorine below the minimums in the table above.
• Free chlorine above 10 ppm while swimmers are in the water.
• A cyanuric acid to free chlorine ratio above 45 to 1, in pools using stabilizer.
• pH below 6.5 or above 8.0.
• Cyanuric acid at 300 ppm or more. The pool must close and stay closed until the CYA is brought down (5.7.3.1.3.3, 6.6.3.1).

How does stabilizer change the minimum? A worked example

Say an outdoor pool uses stabilizer, and the monthly test shows cyanuric acid at 60 ppm. Two MAHC rules apply:

1. The stabilizer minimum is 2.0 ppm free chlorine.
2. The ratio must not go above 45 to 1. 60 divided by 45 is about 1.3 ppm.

The higher number wins: 2.0 ppm. Now say the cyanuric acid creeps up to 90 ppm. 90 divided by 45 is exactly 2.0 ppm, so any free chlorine reading below 2.0 breaks both rules. Above 90 ppm, the pool is past the MAHC cyanuric acid limit. The trained operator decides how to bring it down.

How do you turn the rules into a sheet staff can use?

Make one short reference sheet for each pool and spa. Have your trained operator fill it in from your health code and product label:

Field	What to write
Pool name and type	Pool, spa, wading pool
Stabilizer used?	Yes or no, and the last CYA result
Free chlorine low limit	Number, ppm, code section
Free chlorine high limit	From the product label
pH range	Number and code section
Close-the-pool numbers	From your local code
Who to call	Name and phone of the trained operator
Reviewed	Date and reviewer

Keep a pool and a nearby spa on separate lines, since the spa minimum is higher. If the code and label seem to conflict, ask the health department.

Why do you need to record pH too?

CDC's water treatment page says chlorine kills germs less well as pH goes up, especially above 8.0. Record chlorine and pH from the same test round.

What should happen when a reading is outside the limits?

If a reading breaks a close-the-pool number, clear the water and call the trained operator. If it is out of range but not at a closing number, call the trained operator and retest after their fix. See what to do when chlorine is dropping. In both cases, follow your training, the product label and your health department. For a chemical release or injury, follow the emergency plan and call 911.

Record the first result, who you told, and each retest as its own entry. Leave chemical doses off the sheet; they depend on your pool, product and equipment.

How often should you test?

Before opening each day, test free chlorine, combined chlorine (or total bromine) and pH (MAHC 5.7.5.1). While open, test free chlorine (or bromine) and pH again every 2 hours with a hand-fed system, or every 4 hours with an automatic controller (5.7.5.2, 5.7.5.3). See how often to test commercial pool water.

Poolean keeps water readings, test photos and closures in each pool's record. See the water testing features or book a 30-minute call.

The short version

• 2024 MAHC free chlorine floors: 1.0 ppm, 2.0 ppm with stabilizer, 3.0 ppm in spas.
• The ceiling comes from the product label; above 10 ppm with swimmers in, the MAHC says close.
• Keep pH between 7.0 and 7.8 and cyanuric acid at or below 90 ppm under the MAHC.
• Your state or county code wins, so write its numbers and sections on each pool's sheet.