Dose your pool shock correctly. Calculate amounts for liquid bleach, Cal-Hypo, and Dichlor to maintain a healthy swimming environment. Whether you are dealing with a green pool or just doing a weekly maintenance shock, our tool ensures you hit your target levels accurately.
Shocking means driving free chlorine high enough to destroy chloramines, bacteria, and algae, so this tool needs your pool volume in gallons or litres, your current free-chlorine reading, and a target shock level. For routine maintenance shock aim for 5-10 ppm; for visible algae 10-12 ppm; and for stubborn yellow or black algae 20-30 ppm. Critically, enter your cyanuric acid (CYA), because stabilizer blunts chlorine's strength: the breakpoint and algae-killing targets scale with CYA, so a pool at 50 ppm CYA needs far more chlorine to reach an effective free-chlorine ratio than one at 20 ppm. Choose your product, since each carries a different available-chlorine percentage: 12.5% liquid chlorine, about 65-73% cal-hypo, or roughly 56% dichlor (which also adds CYA). Test late in the day and shock at dusk so sunlight does not burn off the dose before it works.
The core relation: ounces or grams = volume x desired ppm rise x a product factor. For 12.5% liquid chlorine, about 10.7 fl oz per 10,000 gal raises FC 1 ppm. Worked example: a 15,000 gal (56,800 L) pool reading 1 ppm FC, shocking to 12 ppm, needs an 11 ppm rise. That is 10.7 fl oz x (15,000/10,000) x 11 = about 176 fl oz, roughly 1.4 US gallons (5.3 L) of liquid chlorine. With cal-hypo at 65%, roughly 2 lb per 10,000 gal raises FC about 10 ppm, so an 11 ppm rise in 15,000 gal needs about 2 x 1.5 x 1.1 = 3.3 lb (1.5 kg). Dichlor reaches the same level with more product and adds CYA each time. Pour or pre-dissolve, then broadcast in front of a running return jet for one full turnover.
Getting the dose right matters because under-shocking wastes chemicals and lets algae rebound, while over-shocting bleaches vinyl liners and corrodes fittings. CDC Healthy Swimming guidance is clear that swimmers must stay out until free chlorine falls back to about 1-4 ppm, typically the next day, so test before re-entry. Never mix shock types in one bucket and never add cal-hypo and liquid chlorine together, since the reaction can ignite or release chlorine gas. Always add product to water, not water to product, with the pump running and the filter on. Common mistakes include shocking at noon (sunlight destroys unstabilized chlorine within hours), ignoring high CYA that makes your target unreachable, and shocking a pool with low pH that wastes sanitizing power. Retest 24 hours later and rebalance pH, which most shocks temporarily raise.
Liquid chlorine is the cleanest option as it adds no extra minerals. Cal-Hypo is great if your calcium is low. Dichlor is convenient but adds significant amounts of stabilizer (CYA).
For mild algae, you typically need to hit 10-12 ppm. For severe black or yellow algae, you may need to reach 20-25 ppm depending on your current CYA level.
Yes, most shocks will temporarily raise your pH. It's best to re-test and balance your pH 24 hours after a heavy shock treatment.