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Three kinds of shock
Routine shock
A weekly or after-party boost to burn off sweat, sunscreen and other organics. A level around 10 ppm (or a bit more with higher stabilizer) is plenty for a pool that is otherwise clear.
Breakpoint chlorination (chlorine smell, red eyes)
That strong "chlorine" smell actually comes from chloramines, chlorine that has combined with contaminants. To destroy them, raise free chlorine by about 10 times your combined chlorine reading. Below that, you can make the smell worse.
Clearing algae (green or cloudy pool)
Algae dies only if chlorine stays high for long enough. With stabilizer in the water, that means keeping free chlorine at about 40% of your CYA (at least 10 ppm) until the water is clear, combined chlorine is 0.5 ppm or less and the pool loses less than 1 ppm of chlorine overnight. Expect to re-dose several times a day for a few days. Follow our green pool guide step by step.
Why liquid chlorine is usually the best shock
"Shock" bags are usually cal-hypo or dichlor. Using them repeatedly adds calcium or a lot of stabilizer: shocking to 15 ppm with dichlor adds about 13 ppm of CYA, which makes the next shock even harder. Liquid chlorine adds no stabilizer or calcium, so it is the first choice for big or repeated shocks.
Safety first: Always read the product label. Add chemicals to water, never water to chemicals. Add one chemical at a time with the pump running, never mix products (especially chlorine and acid), and keep everyone out of the water until levels are back in range. Wear gloves and eye protection when handling acid or shock.
Sources and methodology
Last reviewed: November 2026. Doses are calculated from the chemistry of each product (molecular weights and available chlorine) and cross-checked against manufacturer and industry dosing charts. Recommended ranges follow CDC guidance for home pools and hot tubs.
- CDC – Home pool and hot tub water treatment and testing
- Orenda – Sodium hypochlorite (liquid chlorine) technical notes
Frequently asked questions
How much shock do I need for a green pool?
Enough to hold free chlorine at about 40% of your CYA level (for example 16 ppm with 40 ppm CYA) until the water is clear, combined chlorine is 0.5 ppm or less and you lose less than 1 ppm overnight. That usually takes several days of re-dosing.
What is breakpoint chlorination?
Raising free chlorine by about 10 times your combined chlorine reading to destroy chloramines, the compounds behind the 'chlorine smell' and red eyes.
Should I shock at night?
Yes. Sunlight destroys unprotected chlorine quickly, so shocking at dusk lets it work for hours.