Water Sanitation

How to Shock a Pool: Clear Green & Cloudy Water in 24 Hours

Shocking your pool (superchlorination) destroys organic debris, chloramines, and stubborn algae. Follow this practical guide to calculate your exact chemical dosage and restore crystal clarity safely.

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Our shock calculator computes exact Cal-Hypo, Dichlor, or Liquid Chlorine doses.

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The 5-Step Process to Shocking Your Pool

Step 1: Balance Your pH & Alkalinity First

Chlorine effectiveness is dictated by pH. If your pH is 8.0, chlorine is only 20% effective! Adjust pH down to 7.2–7.4 before shocking for maximum killing power.

Step 2: Clean and Brush the Pool

Remove large leaves and debris with a skimmer net. Algae forms a protective biofilm barrier on walls and floor; scrub it thoroughly with a stiff nylon pool brush so the shock can penetrate.

Step 3: Calculate Dosage & Apply at Dusk

Wait until sunset. Pre-dissolve Cal-Hypo shock granules in a 5-gallon bucket of pool water (never add water to chemical—always chemical to water), then pour slowly around the deep end returns.

Step 4: Run Pump on Continuous 24-Hour Cycle

Keep the filtration system running non-stop. Dead algae will turn water into a milky grey/blue color. Clean or backwash your filter cartridge or sand once filter pressure rises by 8–10 PSI.

Step 5: Retest Before Anyone Swims

Test Free Chlorine after 12–24 hours. Swimmers may re-enter once FC drops below 5 ppm and water clarity is restored so the main drain is clearly visible.

Recommended Pool Shock & Testing Supplies

For fast clearing without raising Cyanuric Acid (CYA), choose 68–73% Calcium Hypochlorite or commercial liquid pool chlorine.

Shop Cal-Hypo Pool Shock →Shop Taylor K-2006 FAS-DPD Test Kit →

Frequently Asked Questions About Shocking Pools

Always shock your pool in the evening or at night after sunset. Ultraviolet rays from the sun degrade unstabilized chlorine rapidly, wasting up to 50% of your shock within just two hours.
Do not swim until Free Chlorine (FC) levels return to the safe swimming window between 1.0 and 4.0 ppm, and your pH is between 7.2 and 7.6. This typically takes 12 to 24 hours.
For light green algae, double your normal shock dose (target 10–15 ppm FC). For dark green or black algae, triple or quadruple the dose (target 20–30 ppm FC) and brush vigorously.
For vinyl liner and fiberglass pools, always pre-dissolve granular shock in a bucket of pool water first, or use liquid chlorine. Direct contact with granular Cal-Hypo will bleach and ruin vinyl liners.