Pool shock calculator
Shocking means raising free chlorine high enough to kill algae and burn off contaminants. The right target depends on your CYA — enter it and your pool volume to get the exact amount.
How much shock do I need?
Shock to about 40% of your cyanuric acid (CYA) level in free chlorine. For example, at CYA 40 you shock to roughly 16 ppm free chlorine. This “shock level” keeps chlorine strong enough to overcome the algae or contaminants holding your water hostage. The calculator computes the exact product amount for your volume.
Liquid chlorine vs cal-hypo for shocking
Liquid chlorine (sodium hypochlorite) is fast, doesn’t add CYA or calcium, and is ideal for routine shocking. Cal-hypo is a strong granular option but adds calcium over time. Avoid dichlor/trichlor for shocking — they pile on CYA.
Shocking to clear green or cloudy water
For an algae bloom, raise to shock level and hold it there — re-test and re-dose every few hours until free chlorine holds overnight, brushing and running the filter the whole time. See our green-pool guide for the full process.
Ideal ranges
| Level | Target | Notes |
|---|---|---|
| CYA 30 | Shock to ~12 ppm | |
| CYA 40 | Shock to ~16 ppm | |
| CYA 50 | Shock to ~20 ppm | |
| CYA 80 (salt) | Shock to ~32 ppm |
Frequently asked questions
How long after shocking can I swim?
Wait until free chlorine drops back to your normal range (about 1–3 ppm for low CYA). With liquid chlorine this is often the next day; test before swimming.
Why does my chlorine disappear after shocking?
If chlorine vanishes within hours, you likely have an active algae or organic demand — keep holding shock level until it holds overnight. If you have no CYA, sunlight is burning it off; add stabilizer.
Related calculators & guides
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