Pool Shock Calculator
Use this calculator to determine the appropriate amount of pool shock needed to raise your pool's free chlorine (FC) level to your desired target.
Understanding Pool Shock
Pool shock is a concentrated form of chlorine or other oxidizer used to rapidly increase the free chlorine level in your pool water. This process, known as "shocking" or "superchlorination," is crucial for maintaining a healthy and clear swimming environment.
Why Shock Your Pool?
- Eliminate Algae: If your pool water starts to turn green, yellow, or black, shocking is often the first step to kill algae blooms.
- Break Down Chloramines: When chlorine combines with contaminants like sweat, urine, and lotions, it forms "chloramines" (combined chlorine). These are responsible for the strong "chlorine smell" and can cause eye and skin irritation. Shocking breaks down chloramines, freeing up chlorine to sanitize effectively.
- Clear Cloudy Water: Cloudy water can be caused by various factors, including insufficient filtration, high pH, or organic matter. Shocking helps oxidize these contaminants, making them easier for your filter to remove.
- After Heavy Use or Rain: A large number of swimmers or significant rainfall can introduce more contaminants into the pool, depleting chlorine levels. Shocking helps restore sanitation.
- Regular Maintenance: Many pool owners shock their pools weekly or bi-weekly as part of a routine maintenance schedule to prevent problems before they start.
Types of Pool Shock
Different types of pool shock have varying active ingredients and properties:
- Calcium Hypochlorite (Cal-Hypo): A popular and effective choice, typically containing 65-75% active chlorine. It's strong and relatively inexpensive but adds calcium to the water, which needs to be monitored to prevent scaling. It should be dissolved in a bucket of water before adding to the pool, and added at dusk to prevent UV degradation.
- Dichlor (Sodium Dichloro-s-triazinetrione): Contains 50-60% active chlorine and is stabilized, meaning it contains cyanuric acid (CYA). This helps protect chlorine from UV rays. It's pH neutral and dissolves quickly, making it easy to use. However, continuous use can lead to high CYA levels.
- Lithium Hypochlorite: Contains 30-35% active chlorine. It dissolves very quickly and doesn't add calcium or CYA. It's more expensive and less potent than Cal-Hypo or Dichlor.
- Non-Chlorine Shock (MPS – Monopersulfate): An oxidizer that doesn't contain chlorine. It breaks down chloramines and organic contaminants but doesn't sanitize or kill algae like chlorine shock. It's good for regular oxidation without raising chlorine levels significantly, allowing swimming sooner.
How to Use the Calculator
- Enter Pool Volume: Input the total volume of your pool in gallons. If you don't know it, you can estimate it based on your pool's dimensions (e.g., for a rectangular pool: Length x Width x Average Depth x 7.5 = Gallons).
- Enter Current Free Chlorine (FC): Use a reliable test kit to measure your pool's current free chlorine level in parts per million (ppm).
- Enter Target Free Chlorine (FC): This is the ppm level you want to reach. For routine shocking, 10-20 ppm is common. For severe algae, you might aim for 20-30 ppm or even higher.
- Enter Shock Active Chlorine %: Check the label of your pool shock product for its active chlorine percentage. Common values are 68% for Cal-Hypo or 56% for Dichlor.
- Click "Calculate Shock Amount": The calculator will provide the estimated amount of shock (in pounds) you need to add.
Important Considerations & Safety Tips
- Test Your Water: Always test your water's pH, alkalinity, and CYA levels before and after shocking. Adjust as needed.
- Shock at Dusk: Chlorine is quickly degraded by sunlight. Adding shock in the evening allows it to work more effectively overnight.
- Dissolve First (for Cal-Hypo): Always pre-dissolve Cal-Hypo shock in a bucket of water before adding it to the pool to prevent bleaching or damage to pool surfaces.
- Run Your Pump: Keep your pool pump running for at least 8-12 hours after shocking to ensure proper circulation and filtration.
- Retest: After 12-24 hours, retest your free chlorine level to ensure it has returned to a safe swimming range (1-3 ppm) before allowing swimmers.
- Safety First: Always wear protective gloves and eyewear when handling pool chemicals. Never mix different types of shock or other chemicals directly. Add chemicals to water, not water to chemicals.