Calculator
Chlorine Dose & Shock Calculator
Chlorine dosing is arithmetic, not guesswork: product strength, pool volume and the ppm you need to gain. Enter your numbers to get the dose for four common products, plus the breakpoint shock level for your stabilizer reading.
gal
ppm
ppm
Result
Add 40.1 fl oz
Liquid chlorine (12.5%) to raise free chlorine by 2.5 ppm. Add with the pump running and retest in 6–8 hours.
- Target free chlorine
- 3.0 ppm
- Minimum FC for this CYA
- 3.0 ppm
- Breakpoint shock level
- 16.0 ppm
- Adds CYA?
- No
How this is calculated
- Free chlorine should sit between 1 and 3 ppm in a stabilized residential pool, and never below 7.5% of the cyanuric acid (CYA) level.
- Dose per 10,000 gallons to gain 1 ppm: about 1.8 oz cal-hypo (73%), 2.4 oz dichlor (56%), 1.5 oz trichlor (90%), or 10.7 fl oz liquid chlorine (12.5%).
- Breakpoint shock target = roughly 40% of the CYA reading, with a 10 ppm floor. Below that threshold, chloramines are not fully broken down and the pool keeps smelling of chlorine.
- Dichlor and trichlor add CYA as they dissolve (dichlor about 9 ppm CYA per 10 ppm chlorine), so they are poor choices for repeated shocking.
- Add product with the pump running, and retest 6 to 8 hours later rather than immediately.
Figures follow commonly published residential pool references and are guidance, not a substitute for testing your own water. Always follow the product label and add one chemical at a time.
Frequently asked
- How much shock does a green pool need?
- Bring free chlorine to the breakpoint target for your CYA level and hold it there until the water clears, which usually means repeat doses over two to four days plus continuous filtration and brushing. A neglected green-to-clean recovery often needs several times the volume of a routine shock.
- Should I use liquid chlorine or cal-hypo?
- Liquid chlorine adds no CYA or calcium, which makes it the cleaner choice for frequent dosing and for shocking. Cal-hypo stores longer and adds calcium hardness, useful in soft-water regions but a problem in hard-water or high-calcium pools.
- Why does chlorine disappear so fast?
- The usual causes are low CYA (unstabilized chlorine burns off in sunlight within hours), a high chlorine demand from organics or algae, or very high CYA masking the chlorine that is present. Test CYA before assuming the sanitizer is at fault.
- How long before it is safe to swim?
- Wait until free chlorine drops back under about 4 ppm and pH is between 7.2 and 7.8. After a heavy breakpoint shock, that is typically 12 to 24 hours with the pump running.
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