Pool Shock Calculator
Calculate exactly how much shock to add for algae treatment, cloudy water, or routine maintenance. Get dosages based on your pool size and CYA level.
0 for non-stabilized pools
Weekly shock maintains water quality
Choose your shock product:
Liquid Chlorine
12.5% Sodium Hypochlorite
Best for routine shock - no CYA added
1.8 gallons
Cal-Hypo Shock
65% Calcium Hypochlorite
Adds calcium - avoid with hard water
2.8 lbs
Dichlor Shock
56% Sodium Dichlor
Adds CYA - watch stabilizer levels
3.5 lbs
Shock Instructions:
- • Shock at dusk or night (sunlight destroys chlorine)
- • Run pump for 8+ hours after shocking
- • Wait until FC drops below 5 ppm before swimming
- • For algae: brush pool before and after shocking
When and How to Shock Your Pool
Shocking your pool raises chlorine to levels that destroy algae, bacteria, and chloramines that regular chlorination can't handle. Understanding when and how to shock is essential for pool maintenance.
When to Shock Your Pool
Shock once a week during swimming season to oxidize contaminants and prevent algae.
Green, yellow, or black algae requires aggressive shocking at 30-40% of CYA level.
Hazy or milky water often indicates organic buildup that oxidation can clear.
A strong "chlorine smell" means combined chlorine is high - breakpoint chlorination is needed.
Pool parties or heavy bather load introduce contaminants that need oxidation.
The CYA Factor
Cyanuric acid (CYA/stabilizer) protects chlorine from sunlight but also makes it less effective. Higher CYA requires higher shock levels:
| CYA Level | Shock Target | Algae Treatment |
|---|---|---|
| 0 (no stabilizer) | 10 ppm | 10-15 ppm |
| 30 ppm | 12 ppm | 12-18 ppm |
| 50 ppm | 20 ppm | 20-30 ppm |
| 70+ ppm | 28 ppm | 28-40 ppm |
Pro Tip: If your CYA is above 70-80 ppm, shocking becomes very expensive and less effective. Consider partial drain and refill to lower CYA before treating algae.
Frequently Asked Questions
How much shock do I need for my pool?
The amount depends on your pool size, current chlorine level, CYA (stabilizer) level, and why you're shocking. For routine weekly shock, target 10 ppm. For algae treatment, you may need to reach 30-40% of your CYA level to be effective.
What is breakpoint chlorination?
Breakpoint chlorination is the point where you add enough chlorine to destroy all combined chlorine (chloramines) and organic matter. This typically requires raising free chlorine to 10x the combined chlorine reading, or about 10+ ppm.
Should I shock my pool weekly?
Weekly shocking is recommended for most residential pools during swimming season. It helps eliminate chloramines, prevent algae growth, and oxidize contaminants that regular chlorination may miss.
What is the best time to shock a pool?
Shock your pool at dusk or after dark. Sunlight rapidly destroys unstabilized chlorine - you can lose up to 90% within 2 hours. Shocking at night allows the chlorine to work for 8-12 hours before sunrise.
Can I swim after shocking my pool?
Wait until free chlorine drops below 5 ppm before swimming, typically 8-24 hours. Test the water before allowing swimmers in. High chlorine can irritate eyes, skin, and damage swimwear.
What's the difference between shock types?
Liquid chlorine (sodium hypochlorite) is fast-acting and doesn't add CYA. Cal-hypo is powerful but adds calcium. Dichlor contains CYA which can build up over time. Non-chlorine shock (MPS) oxidizes without adding chlorine, good for spas.
Learn More About Pool Chemistry
More Pool Chemistry Tools
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