What Is Free Chlorine, And How Is It Different From Total Chlorine?

Free chlorine refers to the amount of active chlorine available to sanitize the water. Total chlorine includes both free chlorine and combined chlorine (chloramines). If total chlorine is significantly higher than free chlorine, it's time to shock the water to remove chloramines.

What Is Free Chlorine?

Free chlorine is the portion of chlorine available to sanitize your water. It destroys bacteria, breaks down algae, and keeps your water safe for swimmers.

You can think of free chlorine as the "working" chlorine.

• It is added through tablets, granules, or liquid

• Should be tested regularly (ideal range: 1 to 3 ppm for pools, 3 to 5 ppm for hot tubs)

• Gets used up over time as it works on contaminants

What Is Total Chlorine?

Total chlorine is the sum of:

• Free chlorine (the sanitizer that is still active)

• Combined chlorine (chlorine that has already reacted with contaminants)

When total chlorine is higher than free chlorine, the difference is the amount of combined chlorine in the water.

What Is Combined Chlorine?

Combined chlorine forms when free chlorine reacts with sweat, urine, body oils, and other organic waste. It is less effective and can cause eye irritation or that strong chlorine smell.

• Also called chloramines

• Indicates water needs to be shocked

• Ideally kept below 0.2 ppm

Why Does The Difference Matter?

Maintaining a proper level of free chlorine ensures effective sanitation. If combined chlorine builds up, it means your water is struggling to stay clean.

Key reasons this matters:

• Water may look clean but still contain harmful bacteria

• Too much combined chlorine means unpleasant smells

• Sanitizer will be less effective

How To Test Free And Total Chlorine

Use a good-quality water test kit or test strips that measure both.

• Dip test strip into water and match to color chart

• Digital testers are more accurate but cost more

• Always test at least twice a week for pools, more often for hot tubs

When testing:

• If total chlorine equals free chlorine: Water is good

• If total chlorine is greater than free chlorine: Shock your water

How To Fix High Combined Chlorine

When combined chlorine is too high, it means your free chlorine is being used up but not replenished. Here’s how to fix it:

1. Shock The Water

• Use a chlorine shock product (calcium hypochlorite or dichlor)

• Follow instructions for dose based on pool or tub size

• Leave the cover off to allow gases to escape

2. Increase Circulation

• Run your pump longer

• Make sure filters are clean

• Brush walls to stir up stagnant areas

3. Retest After 24 Hours

• Ensure combined chlorine is below 0.2 ppm

• If not, repeat shock treatment

How To Prevent Chlorine Imbalance

Prevention is the best strategy for clean, balanced water.

• Test chlorine levels 2 to 3 times weekly

• Shock weekly or after heavy use

• Keep pH between 7.2 and 7.8 for chlorine to work properly

• Clean or replace filters as needed

• Limit organic waste by showering before use

Quick Reference Summary

• Free Chlorine is the active sanitizer. Ideal range: 1 to 3 ppm for pools, 3 to 5 ppm for hot tubs.

• Combined Chlorine is the used-up chlorine. Should stay below 0.2 ppm.

• Total Chlorine is the sum of both. If higher than free chlorine, it’s time to shock.

Understanding the relationship between free and total chlorine helps you keep water safe, clear, and inviting. Keep up with testing and maintenance to avoid issues before they start.