How much shock to add to your pool
Shocking just means raising free chlorine high enough, fast enough, to burn through algae and organics that a normal dose can't. How much you need comes down to your pool's volume and getting to shock level.
What “shock level” means
Shocking isn't a special chemical so much as a target: push free chlorine up to 10–15 ppmand hold it there. That's well above the everyday 1–3 ppm, high enough to break down chloramines (the source of that harsh chlorine smell) and kill an algae bloom. You dose to close the gap between your current reading and shock level — the bigger the gap and the pool, the more you add.
When to shock
- Water's gone green or cloudy.
- A strong chlorine smell (that's chloramines — counterintuitively, add more).
- Chlorine keeps crashing to zero (a demand to clear).
- After heavy use — a party, a storm, a heat wave.
Shock at dusk so the sun doesn't burn it off before it works, and run the filter throughout. Re-test and wait until chlorine falls to 3 ppm or below before swimming.
Work out your exact dose
Numbers in hand? This free calculator turns them into the exact amount for your pool's size:
Pool Shock CalculatorHow much shock to add to reach shock level and clear the water.Frequently asked
- What is shock level for a pool?
- Around 10–15 ppm free chlorine — well above the everyday 1–3 ppm. It's high enough to break down chloramines and kill algae. You hold it there until the water clears, then let it fall back.
- How much shock for a 10,000 gallon pool?
- It depends on your current chlorine and the product's strength, but as a feel: reaching shock level in a ~38,000 L (10,000 gal) pool takes several hundred grams of a typical cal-hypo shock. Use your product's dosing figure scaled to your volume for the real number.
- Can you swim after shocking?
- Not immediately. Wait until free chlorine drops back to 3 ppm or below and pH is 7.2–7.6, and always re-test first — going in at shock level means stinging eyes and skin.
- When is the best time to shock?
- At dusk or after dark, with the filter running. Sunlight destroys free chlorine quickly, so shocking in full sun wastes much of the dose before it can work.
More pool help
- Common pool problems — Green, cloudy, low chlorine, drifting pH — what's wrong and how to fix it.
- Why your pool turned green — Green water is algae from low chlorine — the step-by-step fix and how long it takes.
- How much chlorine to add — Hit a safe 1–3 ppm — the rule of thumb, worked examples, and why it won't hold.
- How to lower your pool's pH — Pool pH too high? Why it matters and how to bring it back to 7.2–7.6.
- How to raise your pool's pH — Pool pH too low? Acidic water stings and corrodes — how to bring it back up.
- Cloudy pool water — Clear but not green? The three usual causes and how to get back to clear.
- Chlorine won't hold — Chlorine crashing to zero is a demand to shock out — how to diagnose and fix it.
Stop guessing, start swimming
Algae Later reads your pH and chlorine, tells you exactly what to add, and nudges you when it's time to test again.
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