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Pool Shock Calculator — How Much Shock to Add per Pool Size
Calculate how much pool shock to add for any pool size — green, cloudy, or routine treatment. Dosage charts for cal-hypo and liquid chlorine. No sign-ups. Instant results.
For green pools or persistent algae that don't respond to regular shock, the SLAM method is a more systematic approach — it calculates your CYA-based target and walks you through the full process.
💡 Quick answer — how much shock to add by pool size
Maintenance shock (clear water, raise to 10 ppm):
10,000 gal → 1 lb cal-hypo | 15,000 gal → 1.5 lbs | 20,000 gal → 2 lbs |
30,000 gal → 3 lbs
Green pool shock (raise to 30 ppm):
10,000 gal → 3 lbs cal-hypo | 15,000 gal → 4.5 lbs | 20,000 gal → 6 lbs |
30,000 gal → 9 lbs
Liquid chlorine equivalent: 1 gallon per 10,000 gal for maintenance | 3 gallons per
10,000 gal for green water
Use the calculator below for your exact condition and pool size.
⚠️ Always check and adjust pH to 7.2-7.4 before shocking for maximum effectiveness.
Ready to shock? Shop by type:
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 much shock to add by pool size (cal-hypo)
Pounds of calcium hypochlorite shock (65% available chlorine) needed based on pool size and pool condition.
| Pool size | Maintenance (10 ppm) |
Cloudy water (15 ppm) |
Light green (20 ppm) |
Dark green (30 ppm) |
|---|---|---|---|---|
| 5,000 gal | 0.5 lbs | 0.75 lbs | 1 lb | 1.5 lbs |
| 6,000 gal | 0.6 lbs | 0.9 lbs | 1.2 lbs | 1.8 lbs |
| 10,000 gal | 1 lb | 1.5 lbs | 2 lbs | 3 lbs |
| 15,000 gal | 1.5 lbs | 2.25 lbs | 3 lbs | 4.5 lbs |
| 20,000 gal | 2 lbs | 3 lbs | 4 lbs | 6 lbs |
| 25,000 gal | 2.5 lbs | 3.75 lbs | 5 lbs | 7.5 lbs |
| 30,000 gal | 3 lbs | 4.5 lbs | 6 lbs | 9 lbs |
Based on 65% calcium hypochlorite starting from 0 ppm. If you have existing chlorine, subtract it from the target ppm first. Always adjust pH to 7.2–7.4 before shocking — high pH reduces effectiveness by 50%+.
Liquid chlorine shock dosage by pool size
Gallons of liquid chlorine (10% sodium hypochlorite) needed to shock based on pool size and condition.
| Pool size | Maintenance (10 ppm) |
Light green (20 ppm) |
Dark green (30 ppm) |
|---|---|---|---|
| 10,000 gal | 1 gallon | 2 gallons | 3 gallons |
| 15,000 gal | 1.5 gallons | 3 gallons | 4.5 gallons |
| 20,000 gal | 2 gallons | 4 gallons | 6 gallons |
| 25,000 gal | 2.5 gallons | 5 gallons | 7.5 gallons |
| 30,000 gal | 3 gallons | 6 gallons | 9 gallons |
Based on 10% sodium hypochlorite. For 12.5% liquid chlorine, use 80% of the amounts shown. Pour directly into the deep end near a return jet. Always shock after dark for best results.
Pool shock dosage in litres (metric pools)
How much cal-hypo shock (65%) to add for metric pools, by pool size and condition.
| Pool size | Maintenance (10 ppm) |
Light green (20 ppm) |
Dark green (30 ppm) |
|---|---|---|---|
| 20,000 L | 210 g | 420 g | 630 g |
| 40,000 L | 420 g | 840 g | 1,260 g |
| 50,000 L | 525 g | 1,050 g | 1,575 g |
| 75,000 L | 790 g | 1,580 g | 2,370 g |
Formula: pool litres × target ppm × 0.0000153 × 1000 = grams of 65% cal-hypo needed. 1 US gallon = 3.785 litres.
How to shock a pool — step-by-step guide
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. If the pool still won't clear after repeated shocks, the SLAM method uses your CYA level to set a precise chlorine target and walks you through the full multi-day recovery process.
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.
How much shock for a 10,000 gallon pool?
For a 10,000 gallon pool: add 1 pound of cal-hypo (65%) for maintenance shocking, 2 pounds for cloudy or light green water, or 3 pounds for a dark green pool. For liquid chlorine, use 1 gallon for maintenance or 3 gallons for green water. Always adjust pH to 7.2–7.4 before shocking and shock after dark for best results.
How much shock for a 15,000 gallon pool?
For a 15,000 gallon pool: add 1.5 pounds of cal-hypo for maintenance, 3 pounds for light green water, or 4.5 pounds for a dark green pool. For liquid chlorine, use 1.5 gallons for maintenance or 4.5 gallons for green water. Shock after dark and run the pump for 8–24 hours, then test before swimming.
How much shock for a 6,000 gallon pool?
For a 6,000 gallon pool: add 0.6 pounds (about 10 oz) of cal-hypo for maintenance, 1.2 pounds for light green water, or 1.8 pounds for a dark green pool. Small pools are easy to over-shock — measure carefully and retest before swimming.