Pool Shock & Chlorine Calculator
Shocking your pool restores sanitizer and clears cloudy or algae-prone water. Enter your pool volume and how many ppm you want to raise free chlorine to get the dose in both liquid chlorine and cal-hypo.
Pool Shock & Chlorine Calculator
Why use the Pool Shock & Chlorine Calculator
Cloudy, algae-prone or heavily-used water needs a precise chlorine boost. Too little does nothing; too much bleaches liners and swimwear. This scales the dose to your pool.
How to get your numbers
- Volume in gallons (from the Pool Volume Calculator).
- Current free chlorine from a test kit or strips.
- Target rise: about 5 ppm for routine shock, up to 30 ppm to kill algae.
Recommended for this job
How to use it
- Enter your pool volume in gallons.
- Enter how much you want to raise free chlorine (routine shock is about 5 ppm).
- Use whichever product you have — the tool gives both.
Frequently asked questions
How much chlorine do I need to shock my pool?
About 10.7 fl oz of 12.5% liquid chlorine per 10,000 gallons raises free chlorine by 1 ppm. The calculator scales that to your volume and target rise.
Should I use liquid chlorine or cal-hypo to shock?
Liquid chlorine is easy to pour and does not add calcium; cal-hypo is cheaper per dose but raises calcium hardness over time. Both work — the tool gives amounts for each.
When is the best time to shock a pool?
After dusk, so sunlight does not burn off the chlorine before it works, and with the pump running to circulate it.
How much shock do I need to kill algae?
Raise free chlorine to roughly 30 ppm and hold it there until the water clears — the SLAM (Shock, Level, And Maintain) method.
How long after shocking can I swim?
Wait until free chlorine drops back to about 5 ppm or lower — usually several hours to overnight after a normal shock.
Why is my pool still cloudy after shocking?
Usually the filter needs to run longer to clear dead algae and debris, or chemistry (pH, stabilizer) is off. Keep the pump running and re-test.
How often should I shock my pool?
Weekly during peak season is common, plus after heavy use, storms, or any sign of algae or a strong chlorine smell (which signals combined chlorine).
What is the difference between free and total chlorine?
Free chlorine is the sanitizer still available to work; total chlorine includes chlorine already used up. Shocking burns off that used-up “combined” chlorine.
