What Is Free Chlorine vs Total Chlorine?

Understanding the difference between free chlorine and total chlorine is essential for maintaining clean, safe, and properly sanitized pool water. Both are measured in parts per million (ppm), and both play a role in effective pool sanitation.

Free Chlorine (FC)

Free chlorine is the chlorine that is available and active in your water to sanitize and kill bacteria, algae, and other contaminants.

Key Points:

• This is the "working" chlorine doing the job.
• It is what your test strips or kits typically measure first.
• Ideal range: 1–3 ppm for residential pools.

When free chlorine drops too low, the pool is more likely to develop algae or allow bacteria to grow.

Combined Chlorine (CC)

Combined chlorine forms when free chlorine binds with contaminants like sweat, urine, or body oils. These compounds are called chloramines, and they:

• Are responsible for the strong "chlorine smell"
• Cause eye and skin irritation
• Indicate that chlorine is working, but is now used up

Key Point:

Combined chlorine = Total Chlorine – Free Chlorine

Ideal level: 0 ppm (or as close to zero as possible)

If CC is 0.2 ppm or higher, it’s time to shock your pool.

Total Chlorine (TC)

Total chlorine is the sum of:

• Free chlorine (FC)
• Combined chlorine (CC)

It represents all chlorine in the water, both active and used.

Example:

• Free Chlorine: 2.0 ppm
• Combined Chlorine: 0.5 ppm
• Total Chlorine = 2.5 ppm

If your total chlorine is much higher than your free chlorine, it's a sign your pool needs shocking.

Why This Matters

• You want most of your total chlorine to be free chlorine.
• High combined chlorine means poor water quality.
• Regular testing helps keep your sanitizer levels in balance.

How to Test

Use a DPD test kit or digital pool tester to measure both free and total chlorine accurately. Test 2–3 times per week, and always test after heavy use, rain, or chemical adjustments.