How to shock a pool (superchlorination) step by step
When to shock your pool, how much chlorine to use, the safe step-by-step and how long to wait before swimming.
2 min read
Shocking, or superchlorination, means raising chlorine well above normal for a short time. It wipes out algae, chloramines and built-up dirt in one go.
When to do it
- Green water, or water starting to go cloudy.
- Strong chlorine smell and stinging eyes.
- After heavy rain, a pool party, or an accident with feces or vomit in the water.
- When reopening the pool after weeks without use.
How much chlorine
The target is at least 10 ppm of chlorine. If the water has stabilizer, the target goes up: about 40% of the stabilizer level (with 50 ppm of stabilizer, the target is 20 ppm). The calculator works this out for your product and pool size.
Step by step
Bring the pH to between 7.2 and 7.4. At high pH, shocking works poorly.
Do it in the late afternoon or evening: the sun destroys chlorine.
Dissolve chlorine granules in a bucket of pool water (always the product into the water, never water onto the product). Liquid chlorine goes straight in.
With the pump running, pour it in slowly around the edge, spreading it across the pool.
Brush the walls and floor and run the filter for at least 24 hours.
Test the next day. If the water is still green or chlorine has dropped close to zero, repeat.
Nobody in the pool during treatment. Only swim again once chlorine is back to 3 ppm or less, tested with a kit. This usually takes 24 to 48 hours.
In vinyl pools, never throw undissolved granules straight into the water: they settle on the floor and stain the vinyl liner.
The right dose depends on the size of your pool and the product you have. The calculator works it out in spoons and cups.
Calculate the dose now