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Pool Shock Calculator
Calculate how much pool shock to add for green, cloudy, or contaminated water.
Emergency treatment guide for fast pool recovery.
No sign-ups. Instant results.
⚠️ Always check and adjust pH to 7.2-7.4 before shocking for maximum effectiveness.
Example calculation
Let's say you have a 20,000 gallon pool that turned light green overnight (medium shock needed):
| Input | Value |
|---|---|
| Pool volume | 20,000 gallons |
| Pool condition | Light green (medium shock) |
| Target chlorine level | 20 ppm |
| Current chlorine | 0 ppm (assumed) |
| Cal-hypo shock needed | 4 pounds |
| Liquid chlorine needed | 2.5 gallons |
| Wait time | 12-24 hours until chlorine drops below 5 ppm |
Pool shock dosage guide
| Pool Condition | Target Chlorine | Shock Level | When to Use |
|---|---|---|---|
| Clear water (maintenance) | 10 ppm | Light shock | Weekly maintenance, after parties |
| Cloudy water | 15 ppm | Light shock | Slightly cloudy, strong chlorine smell |
| Light green / hazy | 20 ppm | Medium shock | Early algae, pool party aftermath |
| Dark green | 30 ppm | Heavy shock | Green water, visible algae growth |
| Black-green / swamp | 40+ ppm | Extreme shock | Severe algae, can't see bottom |
For best results, always adjust pH to 7.2-7.4 before shocking. High pH reduces shock effectiveness by 50% or more.
How to shock your pool (step-by-step)
Step 1: Test and adjust pH (critical)
Test pH and adjust to 7.2-7.4 using our pH calculator. Shock is 50% less effective at pH 7.8+. Wait 4 hours after pH adjustment before shocking.
Step 2: Calculate shock amount
Use the calculator above based on your pool condition. Measure carefully — under-shocking wastes money and won't clear the pool. Over-shocking is safer than under-shocking for algae.
Step 3: Add shock at dusk
Shock after sunset or at night. UV rays destroy chlorine quickly, reducing effectiveness. For calcium hypochlorite, dissolve in a bucket of pool water first, then pour slowly around the pool perimeter with the pump running. For liquid chlorine, pour directly into the deep end near a return jet.
Step 4: Run the pump overnight
Run your pump for 8-24 hours to circulate shock throughout the pool. Brush walls and floor to distribute chemicals to all surfaces where algae might be hiding.
Step 5: Test before swimming
Wait until chlorine drops below 5 ppm before swimming (typically 12-24 hours). Test with pool test strips to verify. Retest pH and adjust if needed.
Step 6: Follow-up for green pools
If pool is still green after 24 hours, shock again at the same dosage. Vacuum dead algae once pool clears. You may need to add clarifier and clean or backwash the filter.
Pool shock product comparison
🥇 Calcium hypochlorite (cal-hypo)
65-75% available chlorine
Most powerful and cost-effective shock. Best for green pools and heavy algae.
Dissolve before adding. Adds calcium to water.
💧 Liquid chlorine
10-12% available chlorine
Dissolves instantly, easy to use, no calcium. Requires larger volumes.
Shorter shelf life. Great for regular shocking.
⚪ Dichlor granular
55-62% available chlorine
Stabilized (won't degrade in sun), pH neutral, dissolves fast.
More expensive. Best for hot tubs and vinyl pools.
🚫 What NOT to use
Avoid non-chlorine shock for algae
Potassium monopersulfate (non-chlorine shock) oxidizes contaminants but doesn't kill algae.
Only use for maintenance, never for green pools.
Pool shock calculator FAQs
How much shock do I need for a green pool?
For a green pool, you need to raise chlorine to 30 ppm (triple shock). For a 20,000 gallon pool, this requires 3-4 pounds of calcium hypochlorite shock or 3 gallons of liquid chlorine. Always test and adjust pH to 7.2-7.4 before shocking for maximum effectiveness.
How long after shocking can I swim?
Wait until chlorine drops below 5 ppm before swimming. This typically takes 8-24 hours depending on shock amount, sunlight exposure, and pool circulation. Always test with pool test strips before allowing swimmers back in the pool.
What's the difference between shock and regular chlorine?
Shock is highly concentrated chlorine (65-75% available chlorine vs 10-12% for liquid chlorine). Shock quickly raises chlorine to high levels (10-40 ppm) to kill bacteria, algae, and break down contaminants. Regular chlorine maintains daily sanitization at 1-3 ppm. Both are chlorine, just different concentrations.
Can I shock my pool during the day?
Shock at dusk or after dark for best results. UV rays from sunlight break down chlorine quickly (up to 90% in 2 hours), reducing shock effectiveness dramatically. Evening shocking allows chemicals to work overnight without sun degradation.
How often should I shock my pool?
Shock weekly during heavy use or hot weather, every 2 weeks during moderate use, or whenever water becomes cloudy, smells strongly of chlorine (actually chloramines), or tests show combined chlorine above 0.5 ppm. Always shock after heavy rain, pool parties, or if you see algae starting.
Why is my pool still green after shocking?
Common causes: didn't use enough shock (need 30 ppm for green pools), pH was too high (reduces shock effectiveness by 50%+), added shock during the day (sun destroyed it), or filter is clogged with dead algae. Shock again at the correct dosage, clean your filter, and run the pump 24 hours.
Can I use bleach instead of pool shock?
Unscented household bleach (6% sodium hypochlorite) works but requires 2x the volume of pool-grade liquid chlorine (12%). For a 20,000 gallon shock, you'd need 5+ gallons of bleach. Pool shock is more economical and doesn't contain additives that can cause foaming.
How much shock do I need for my pool size?
The amount of shock needed depends on your pool volume. If you don't know your pool size in gallons, use our Pool Volume Calculator first. For most pools, you'll need 1 pound of cal-hypo shock per 10,000 gallons for routine shocking, or 2-3 pounds for severe algae or cloudy water.