01
The purpose
What does this calculator estimate?
Got that chlorine smell? Find your combined chlorine and the shock dose to break past it.
Water Chemistry · B9
Combined Chlorine & Breakpoint Chlorination Calculator
Got that chlorine smell? Find your combined chlorine and the shock dose to break past it.
Measure the inputsThat strong 'chlorine smell' is actually chloramines — a sign of too little chlorine, not too much.
Read the full resultBreakpoint requires hitting the target in a single dose; dribbling chlorine in won't break the bond.
Check the boundaryShock at dusk and run the pump overnight to give the reaction time to complete.
Useful forWater ChemistryPlanningComparisonVerification
Live calculation
Breakpoint dose
✓ Checked May 2026
Enter total and free chlorine to find combined chlorine.
Recommended dose
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Enter the required values to calculate.
Enter the known values. Let the engine handle the calculation.
✓ Formula checked↻ Live result○ No account needed
Planning estimate only. Confirm product labels, equipment specifications, qualified-professional advice and local requirements before acting.
The result, explained
Use the Combined Chlorine & Breakpoint Chlorination Calculator result with context.
Got that chlorine smell? Find your combined chlorine and the shock dose to break past it.
02
The tool
What information does it use?
- Pool volume: enter a measured or verified value
- Total chlorine: From your test kit, in ppm.
- Free chlorine: From your test kit, in ppm.
- Shock product: Cal-hypo or liquid for breakpoint shocking.
03
The method
How to use this calculator
- Pool volumeEnter the value you can verify.
- Total chlorineFrom your test kit, in ppm.
- Free chlorineFrom your test kit, in ppm.
- Shock productCal-hypo or liquid for breakpoint shocking.
04
The relationship
The formula in plain English
Combined chlorine = Total − Free · Breakpoint target FC = Combined × 10
You must hit roughly 10× the combined chlorine in one dose to break the chloramine bond.05
Worked through
A worked example: TC 3.0, FC 2.0 in a 15,000 gal pool
- Combined chlorine = 3.0 − 2.0 = 1.0 ppm
- Breakpoint target = 1.0 × 10 = 10 ppm FC
- Raise FC by 8 ppm → ~1.9 lb cal-hypo 65%
| Combined chlorine | Breakpoint FC target | Cal-hypo 65% dose |
|---|---|---|
| 0.3 ppm | 3 ppm | 0.6 lb |
| 0.5 ppm | 5 ppm | 0.9 lb |
| 0.8 ppm | 8 ppm | 1.5 lb |
| 1.0 ppm | 10 ppm | 1.9 lb |
| 1.5 ppm | 15 ppm | 2.8 lb |
| 2.0 ppm | 20 ppm | 3.8 lb |
06
Why it matters
How the result supports the next decision
That strong 'chlorine smell' is actually chloramines — a sign of too little chlorine, not too much.
Breakpoint requires hitting the target in a single dose; dribbling chlorine in won't break the bond.
07
Good inputs
Improve the estimate before relying on it
- That strong 'chlorine smell' is actually chloramines — a sign of too little chlorine, not too much.
- Breakpoint requires hitting the target in a single dose; dribbling chlorine in won't break the bond.
- Shock at dusk and run the pump overnight to give the reaction time to complete.
- If combined chlorine stays high after shocking, re-test and repeat — heavy loads need a second pass.
- Keep free chlorine in range daily and combined chlorine rarely gets a chance to build up.
08
The boundary
How to interpret the result
Follow the product label, add chemicals separately and retest before another dose.
The engine reports invalid inputs and safety warnings beside the result. Resolve those messages before using the estimate.
09
Before acting
What should override this estimate?
- Measured site conditions and current test results
- Product labels and manufacturer specifications
- Qualified-professional advice and applicable local codes
10
Common questions
Frequently asked questions
What is combined chlorine?
Combined chlorine is chlorine that has already bonded with ammonia and nitrogen from sweat, urine, and organics, forming chloramines. It's the difference between your total and free chlorine readings. Chloramines are weak sanitizers and cause the harsh smell and eye sting people blame on 'too much chlorine.'
What is breakpoint chlorination?
Breakpoint chlorination is adding enough chlorine in one shot to oxidize and destroy chloramines completely. The rule of thumb is to reach about ten times the combined chlorine level. Below that threshold you just make more chloramines; above it, they break apart and clear.
Why does my pool smell strongly of chlorine?
Counterintuitively, a strong chlorine smell means chloramines have built up because there isn't enough free chlorine. The fix is more chlorine, not less — specifically a breakpoint shock to burn off the combined chlorine, after which the smell disappears.
How much chlorine do I need to reach breakpoint?
Multiply your combined chlorine by ten to get the target free chlorine, then dose up to that level. For example, 0.5 ppm combined chlorine needs a 5 ppm FC target. The calculator converts that target into the exact product amount for your pool.
How do I prevent chloramines from forming?
Maintain adequate free chlorine for your CYA level every day, shower before swimming, and discourage urinating in the pool. Regular light shocking and good circulation keep combined chlorine below the 0.2 ppm threshold where problems start.
What combined chlorine level needs shocking?
Anything above 0.2 ppm. At that point chloramines are forming faster than they clear, and a breakpoint shock is due.
Is combined chlorine dangerous?
It's a poor sanitizer and an irritant — it causes red eyes, skin irritation, and the chlorine smell. It's a water-quality problem to fix, not an emergency.
Does non-chlorine shock remove combined chlorine?
Potassium monopersulfate oxidizes some organics but does not reliably break chloramines; a chlorine breakpoint dose is the dependable method.
Primary sources
Use the result with current guidance.
These official references support safe planning context. Product labels, local requirements and qualified-professional advice take priority over a general calculator estimate.