Calculators / Pool
Pool shock calculator: how much shock to use?
Pick why you're shocking and put in your test numbers. You'll get how much to add and how long to stay out.
Updated · How we check our numbers
Shock with this much
2.1 lb of cal hypo
That's 34 oz of 65% cal hypo to take 18,193 gallons up to 10 ppm, superchlorination on the HTH label.
- Pool
- 18,193 gal
- Free chlorine now
- 1 ppm
- Shock to
- 10 ppm
- Granular
- 2.1 lb34 oz
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Estimate for planning only, not professional advice. Check the manufacturer’s instructions, your local code and a licensed professional before you buy, build or install. Use at your own risk. Terms.
surface = 32 ft × 16 ft = 512 sq ft
average depth = (3.5 + 6) ÷ 2 = 4.75 ft
gallons = 512 sq ft × 4.75 ft × 7.48 = 18,193 gal
raise = 10 − 1 = 9 ppm
cal hypo = 18,193 gal × 9 ppm × 8.34 ÷ 1,000,000 ÷ 0.65 = 2.10 lb
Follow the label on pre-dissolving. Granules that sit on a vinyl liner can bleach it.
Shock at dusk. Sun burns chlorine off fast, so a daytime shock loses a lot before it works.
Stay out until free chlorine tests under 10 ppm.
How we work it out
Shock is just a lot of chlorine at once. How much depends on what you're trying to kill.
weekly: raise free chlorine to 10 ppm
smell or cloudy: raise free chlorine by 10 × (total − free)
solid poop: 2 ppm for 25 minutes
diarrhea: 20 ppm for 12.75 hours
The 10 ppm is what the HTH shock label calls superchlorination. Ten times combined chlorine is breakpoint chlorination, from the public pool code. The poop numbers come straight from the CDC, and they assume pH 7.5 or lower with no stabilizer in the water. Stay out until free chlorine drops under 10 ppm.
Where the numbers come from
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