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Pool Shock Calculator

Shocking works only if you hit the right chlorine level for your CYA. Enter your CYA and current chlorine and we'll give you the shock dose.

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How to use it

  1. Test your CYA and current free chlorine.
  2. Enter both plus your volume — the shock target is based on your CYA.
  3. Add liquid chlorine at dusk, keep the pump running, and re-test/re-dose to hold the shock level until the water is clear and chlorine stops dropping overnight.

Why "shock" isn't one number

The old "add 2–3× normal" advice ignores CYA, and that's why shocking often fails. The proven method (SLAM — Shock Level And Maintain) sets the shock target at about 40% of your CYA and holds it there until algae is gone. Higher CYA means a higher shock level. At CYA 40 that's ~16 ppm; at CYA 80 it's ~32 ppm.

Frequently asked questions

How much shock does my pool need?
Enough to reach about 40% of your CYA as free chlorine, then hold it there. For CYA 40 that's ~16 ppm. The dose depends on your current chlorine and volume — enter them above.
How long do I shock for?
Until the water is clear, chlorine holds overnight (loses ≤1 ppm), and any combined chlorine is near zero. That can take several days of re-dosing for a green pool.
Liquid chlorine or cal-hypo for shock?
Liquid chlorine (sodium hypochlorite) is cleanest — it adds no CYA or calcium. Cal-hypo works but adds calcium; dichlor/trichlor add CYA, which you don't want when shocking.

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Built & reviewed by a working pool-service pro. Target ranges follow CDC MAHC, PHTA, and Taylor guidance. Doses are starting estimates — add a little less than the max, re-test, and confirm against your product label. Educational tool, not a substitute for a water test or professional advice.