To shock a 1,000 gallon pool with CYA 40, raise free chlorine from 2 to 16 ppm with 2.9 oz (82 g) of 65% cal-hypo shock. Each 1 lb bag raises free chlorine by 78 ppm in 1,000 gallons. The shock level is 40% of your CYA, so test CYA first.
| From FC 2 to | 65% cal-hypo | 73% cal-hypo | Calcium added |
|---|---|---|---|
| CYA 30 → 12 ppm | 2.1 oz | 1.8 oz | +7 ppm |
| CYA 40 → 16 ppm | 2.9 oz | 2.6 oz | +10 ppm |
| CYA 50 → 20 ppm | 3.7 oz | 3.3 oz | +13 ppm |
| CYA 60 → 24 ppm | 4.5 oz | 4 oz | +16 ppm |
| CYA 80 → 32 ppm | 6.2 oz | 5.5 oz | +21 ppm |
Add
2.9oz
of Cal-hypo shock 65%
82 gabout ⅜ cup by volume
Raises free chlorine from 2 ppm to the shock level of 16 ppm (40% of CYA 40) in 1,000 gal.
Check the product label. Strengths vary by brand, so enter the % printed on yours. Add one chemical at a time, into the water, and never mix chemicals.
Save this test and get reminded when it is time to retest.
Pool Calc for iPhoneComing soon to the App StoreCal-hypo adds calcium: about 0.7 ppm of calcium hardness for every 1 ppm of chlorine. One shock at CYA 40 adds about 10 ppm, which matters in vinyl pools and where the fill water is already hard. If you shock often, 18 fl oz of 10% liquid chlorine does the same job with no calcium.
Dissolve cal-hypo in a bucket of pool water first and pour it in front of a return. Never mix it with any other chlorine product, especially trichlor tablets: the combination can ignite.
A shock (SLAM) is not one dose. Hold free chlorine at the shock level, testing and topping up several times a day, until combined chlorine is 0.5 ppm or less, the overnight loss is 1 ppm or less, and the water is clear.
A 1,000 gallon pool is usually a large inflatable, a stock tank or a small frame pool. Doses this small are easy to overshoot: one extra splash is several ppm. Measure shock with kitchen measures you keep only for pool chemicals, and test after every addition.
Small pools also lose chlorine fast on sunny days because there is so little water. Test daily, and when the numbers drift far off it is often quicker to drain and refill than to correct them.
At CYA 40, about 2.9 oz of 65% cal-hypo, from 2 ppm to the 16 ppm shock level. Each 1 lb bag adds 78 ppm.
Swim when free chlorine is back within your normal range and at or below the re-entry level on your chlorine label (many labels say 4 ppm). Never swim during a SLAM or with free chlorine above 10 ppm. Your product label always comes first.
Both are chlorine. Liquid chlorine adds no calcium or stabilizer, so it suits repeated shocking. Cal-hypo is easier to store but raises calcium hardness.