01
The purpose
What does this calculator estimate?
How much shock to clear chloramines, algae, or cloudy water — sized to your pool and current chlorine.
Water Chemistry · B2
Pool Shock Treatment Calculator
How much shock to clear chloramines, algae, or cloudy water — sized to your pool and current chlorine.
Measure the inputsAlways shock at dusk so chlorine isn't burned off by sunlight before it finishes working.
Read the full resultRun the pump for at least 24 hours after shocking to circulate and filter the water.
Check the boundaryPre-dissolve cal-hypo in a bucket of water for plaster and vinyl pools to avoid bleaching the floor.
Useful forWater ChemistryPlanningComparisonVerification
Live calculation
Shock dose
✓ Checked May 2026
Pick a shock level or set a custom target FC.
Recommended dose
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Enter the required values to calculate.
Enter the known values. Let the engine handle the calculation.
✓ Formula checked↻ Live result○ No account needed
Planning estimate only. Confirm product labels, equipment specifications, qualified-professional advice and local requirements before acting.
The result, explained
Use the Pool Shock Treatment Calculator result with context.
How much shock to clear chloramines, algae, or cloudy water — sized to your pool and current chlorine.
02
The tool
What information does it use?
- Pool volume: enter a measured or verified value
- Shock level: Regular = 10 ppm, triple = 30 ppm, algae = 40 ppm.
- Current free chlorine: From your test kit, in ppm.
- Shock product: Cal-hypo is the most common granular shock.
03
The method
How to use this calculator
- Pool volumeEnter the value you can verify.
- Shock levelRegular = 10 ppm, triple = 30 ppm, algae = 40 ppm.
- Current free chlorineFrom your test kit, in ppm.
- Shock productCal-hypo is the most common granular shock.
04
The relationship
The formula in plain English
Shock dose = (Volume ÷ 10,000) × (Target FC − Current FC) × product constant
Regular shock targets 10 ppm; triple shock 30 ppm; algae clearing 40 ppm.05
Worked through
A worked example: 15,000 gal green pool, triple shock to 30 ppm
- Target increase = 30 − 1 = 29 ppm
- Dose = (15,000 ÷ 10,000) × 29 × 2.0 oz = 87 oz
- 87 oz ÷ 16 = ~5.4 lb cal-hypo 65%, added at dusk
| Pool volume | Regular (10 ppm) | Triple (30 ppm) | Algae (40 ppm) |
|---|---|---|---|
| 5,000 gal | 0.7 lb | 2.0 lb | 2.7 lb |
| 10,000 gal | 1.4 lb | 4.0 lb | 5.4 lb |
| 15,000 gal | 2.0 lb | 6.0 lb | 8.1 lb |
| 20,000 gal | 2.7 lb | 8.1 lb | 10.8 lb |
| 25,000 gal | 3.4 lb | 10.1 lb | 13.5 lb |
| 30,000 gal | 4.1 lb | 12.1 lb | 16.2 lb |
06
Why it matters
How the result supports the next decision
Always shock at dusk so chlorine isn't burned off by sunlight before it finishes working.
Run the pump for at least 24 hours after shocking to circulate and filter the water.
07
Good inputs
Improve the estimate before relying on it
- Always shock at dusk so chlorine isn't burned off by sunlight before it finishes working.
- Run the pump for at least 24 hours after shocking to circulate and filter the water.
- Pre-dissolve cal-hypo in a bucket of water for plaster and vinyl pools to avoid bleaching the floor.
- Don't shock with trichlor — it adds stabilizer fast; use cal-hypo or liquid for shock.
- After shocking for algae, brush the pool and keep FC at the algae level until the water clears.
08
The boundary
How to interpret the result
Follow the product label, add chemicals separately and retest before another dose.
The engine reports invalid inputs and safety warnings beside the result. Resolve those messages before using the estimate.
09
Before acting
What should override this estimate?
- Measured site conditions and current test results
- Product labels and manufacturer specifications
- Qualified-professional advice and applicable local codes
10
Common questions
Frequently asked questions
What does it mean to shock a pool?
Shocking means raising free chlorine high enough — usually 10 ppm or more — to destroy chloramines, kill algae, and oxidize organic waste. It's a temporary spike, not a maintenance level, and you let it fall back to normal before swimming.
How high should I shock for algae?
For visible algae, target around 40 ppm FC and hold it there, brushing daily, until the water is clear and chlorine stops dropping overnight. Lighter green water may clear at 30 ppm. The dose scales with your CYA in a full SLAM.
How much shock do I need for a green pool?
It depends on volume and how green it is. A moderately green 15,000-gallon pool typically needs about 6 lbs of cal-hypo 65% to reach a 30 ppm triple shock from a low starting FC. Heavy algae needs a sustained SLAM, not a single dose.
How long after shocking can I swim?
Wait until free chlorine falls below about 5 ppm — usually 8 to 24 hours depending on sun and starting level. Test before swimming; high shock-level chlorine can irritate skin and eyes and bleach swimwear.
Can I shock with liquid chlorine instead of granular?
Yes. Liquid chlorine is an excellent shock because it adds no calcium or stabilizer. You'll need more volume than concentrated cal-hypo, but it dissolves instantly and won't cloud the water or settle on the floor.
How much shock for a 20,000 gallon pool?
For a regular 10 ppm shock from a 1 ppm start, a 20,000-gallon pool needs about 2.7 lbs of cal-hypo 65%. A triple shock to 30 ppm needs roughly 7.5 lbs.
Is pool shock the same as chlorine?
Most shock is chlorine — cal-hypo or liquid sodium hypochlorite — just used at a much higher dose. Non-chlorine shock (potassium monopersulfate) oxidizes organics but won't kill algae.
How often should I shock my pool?
Most pools benefit from shocking every 1–2 weeks in summer, plus after heavy use, rain, or whenever combined chlorine rises above 0.2 ppm.
Primary sources
Use the result with current guidance.
These official references support safe planning context. Product labels, local requirements and qualified-professional advice take priority over a general calculator estimate.