How Much Chlorine to Shock a Pool
Short answer: raising free chlorine by 10 ppm in a 10,000 gallon pool takes about 0.8 gallons of 12.5% liquid chlorine, 1.7 gallons of 6% bleach or 1.3 lb of 65% cal-hypo. Scale it up or down with the pool size.
What "shocking" a pool means
Shocking means raising free chlorine (FC) well above its normal level for a while, to kill algae, clear cloudy water or break down combined chlorine (the "chlorine smell"). How high you go depends on your stabilizer: pools with more cyanuric acid (CYA) need more chlorine for the same effect. Follow your test kit's chart or the product label for the target; the amounts below show how much product a given rise takes.
The math in one line
Then divide by the strength of the product: liquid chlorine and bleach are sold by trade percent (a gallon of 12.5% liquid holds about 1.04 lb of chlorine), and granular shock by percent of weight. A 1 lb bag of 65% cal-hypo raises 10,000 gallons by about 7.8 ppm.
How much shock to raise free chlorine by 10 ppm
| Pool size | 12.5% liquid chlorine | 10% liquid chlorine | 6% bleach | 65% cal-hypo | 73% cal-hypo |
|---|---|---|---|---|---|
| 5,000 gal | 0.40 gal | 0.50 gal | 0.83 gal | 0.64 lb | 0.57 lb |
| 10,000 gal | 0.80 gal | 1.00 gal | 1.67 gal | 1.28 lb | 1.14 lb |
| 15,000 gal | 1.20 gal | 1.50 gal | 2.50 gal | 1.92 lb | 1.71 lb |
| 20,000 gal | 1.60 gal | 2.00 gal | 3.33 gal | 2.57 lb | 2.28 lb |
| 25,000 gal | 2.00 gal | 2.50 gal | 4.16 gal | 3.21 lb | 2.86 lb |
| 30,000 gal | 2.40 gal | 3.00 gal | 5.00 gal | 3.85 lb | 3.43 lb |
For a 5 ppm rise, halve the amounts; for 20 ppm, double them. Don't know your pool size? Work it out with the pool volume calculator.
Everyday dosing: a smaller pool example
A 6,000 gallon above-ground pool reads 1 ppm and you want 4 ppm. The rise is 3 ppm: 3 × 6,000 × 8.34 ÷ 1,000,000 = 0.15 lb of chlorine. That is about 18 fl oz of 12.5% liquid chlorine or 38 fl oz of 6% bleach. Shocking the same pool by 10 ppm takes about 0.48 gallons of 12.5% liquid or 0.77 lb of 65% cal-hypo.
Which shock to use
- Liquid chlorine or plain bleach raise chlorine without adding stabilizer or calcium. Use unscented bleach with no additives, and check the date: liquid chlorine loses strength in heat and storage.
- Cal-hypo is convenient and strong, but each dose adds calcium hardness. Pre-dissolve it in a bucket of water, especially in vinyl liner pools.
- Dichlor shock adds stabilizer (about 0.9 ppm CYA per 1 ppm of chlorine). Fine for a stabilizer-free pool, but repeated shocking with it builds CYA fast.
How to shock safely
- Test first: free chlorine, pH and, if you can, CYA. Chlorine works best with pH around 7.2 to 7.6.
- Shock in the evening so sunlight does not burn off the chlorine.
- Run the pump and pour liquid in front of a return jet, or broadcast pre-dissolved granules around the pool.
- Never mix different chlorine products or chlorine and acid in the same bucket.
- Test again before swimming. Wait until free chlorine is back in the range your test kit recommends.
Saltwater pool? The generator makes chlorine from salt; keep the salt level right with the pool salt calculator and shock the same way when needed.
Try the pool chlorine calculator
Enter your own numbers below, or open the full pool chlorine calculator with the formula and more examples.
Frequently asked questions
How much liquid chlorine do I need to shock a 10,000 gallon pool?
About 0.8 gallons of 12.5% liquid chlorine raises free chlorine by 10 ppm in 10,000 gallons. With 10% liquid it is about 1 gallon.
How many bags of shock do I need for my pool?
A 1 lb bag of 65% cal-hypo raises 10,000 gallons by about 7.8 ppm. For a 10 ppm rise in 20,000 gallons you need about 2.6 lb, so 3 bags.
How much bleach do I need to shock a pool?
About 1.7 gallons of 6% bleach raises a 10,000 gallon pool by 10 ppm. Use plain, unscented bleach.
How much chlorine for a 6,000 gallon pool?
To raise free chlorine by 3 ppm, about 18 fl oz of 12.5% liquid chlorine or 38 fl oz of 6% bleach.