Easy Pool Calc

How much shock for a 10,000 gallon pool?

Short answer

To shock a 10,000 gallon pool from 1 ppm up to 10 ppm you need about 1.16 lb (18.5 oz) of 65% cal-hypo, which is 2 bags of 1 lb.

How to work it out

  1. In short: raise chlorine from where it is to the shock level, then work out how much of your product holds that much chlorine.
  2. Shock level: 10 ppm
  3. 10 − 1 = 9 ppm × 37,854 L = 341 g of chlorine
  4. 341 g ÷ 65% = 1.16 lb (18.5 oz) = 1.16 bags → 2 bags

A “1 lb bag per 10,000 gallons” is the rule printed on most shock bags, and it is a good start for a routine shock. Whether one bag is enough depends on where chlorine started and on the strength — 65% and 73% bags behave differently.

Adjust for your project

gal
Don’t know it? Work it out with the pool volume calculator or the above-ground pool calculator.
“Available chlorine” on the bag.
ppm
Don’t know it? CYA (stabilizer, cyanuric acid) is what shields chlorine from sunlight — see pool words explained. Most test strips have a CYA pad, and pool stores test it free. The SLAM level is 40% of CYA, so test before a SLAM. For the CDC accident response, CYA must be 15 ppm or less.
Chlorine works better at pH 7.2–7.5. If pH is high, lower it first — the result tells you how much acid.
ppm
More options: Bag size
Add this much shock1.16 lb (18.5 oz)
Bags
2 bags · 1 lb bag
Shock level
10 ppm
Then
Let it fall back to your normal level before swimming — many labels say 4 ppm or less.
Calcium hardness this adds
6.4 ppm
Chemical safetyFollow the product label. Add chemicals to water, never water to chemicals. Never mix chemicals — especially chlorine and acid, or different types of chlorine. Add one at a time with the pump running, keep them away from children, and don’t swim until levels are back in range. This is an estimate: add it, let it circulate, then retest before adding more. Pool and spa water only — never use these doses for drinking water.

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5-gallon bucket (one per chemical)Many shock labels say to pre-dissolve in a bucket of pool water — add the shock to the water, never water to the shock — so granules don’t bleach a liner.
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Bags of 65% cal-hypo to reach 10 ppm, by pool size

Bags of 65% cal-hypo to reach 10 ppm, by pool size
PoolAdd this much shockBags
5,000 gal9.2 oz1 bag
10,000 gal1.16 lb (18.5 oz)2 bags
15,000 gal1.73 lb (27.7 oz)2 bags
20,000 gal2.31 lb (37 oz)3 bags
25,000 gal2.89 lb (46.2 oz)3 bags
30,000 gal3.47 lb (55.5 oz)4 bags

One bag or two?

A 1 lb bag of 65% cal-hypo adds about 7.8 ppm to 10,000 gallons; a 73% bag about 8.7 ppm. So if chlorine is already at 2–3 ppm, one bag takes you to roughly 10 ppm. If it is near zero, one bag gets you to about 8 ppm and part of a second bag finishes the job.

  • Pre-dissolve. Most cal-hypo labels say to dissolve the bag in a bucket of pool water first and pour it around the deep end. Add the granules to the water, never water to the granules.
  • Calcium. Each bag adds about 5–6 ppm of calcium hardness to 10,000 gallons. Weekly shocks add up over a season in hard-water areas.
  • Stabilized pool with algae? A routine 10 ppm shock is too low to clear algae with 40+ ppm of CYA — use the SLAM level instead (16 ppm at 40 CYA) and expect to repeat it.
  • Timing. Shock at dusk, run the pump overnight, and retest in the morning before anyone swims.

Prefer liquid? The same shock from a jug is on how much liquid chlorine to shock a 10,000 gallon pool. A bigger pool is on how many bags of shock for a 20,000 gallon pool.

Different size? Use the full Pool Shock Calculator.

What you’ll need

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Frequently asked questions

How much 73% shock for a 10,000 gallon pool, to 10 ppm?

About 1.03 lb (16.5 oz), which is 2 bags of 1 lb.

How much shock for a green 10,000 gallon pool with 40 ppm CYA?

To the SLAM level of 16 ppm: about 1.93 lb (30.8 oz) of 65% cal-hypo (2 bags) for the first dose, then more each day to hold it. Liquid chlorine is the usual choice for that.

How much dichlor shock for a 10,000 gallon pool?

About 1.34 lb (21.5 oz) of 56% dichlor to reach 10 ppm, adding about 8.2 ppm of stabilizer.

Other common sizes

Sources