A swimming pool stays clear and hygienic when two things are right: the water is sanitised and the pH is in range. This guide covers how to shock a pool to restore clear water and how to keep the pH balanced so the chlorine can do its job.
What pool shocking means
Shocking a pool means adding a high dose of chlorine in one treatment to rapidly destroy bacteria, algae, chloramines and organic matter that normal day-to-day chlorination leaves behind. Hypo Pool Shock is a high-strength calcium hypochlorite granule for exactly this. It releases a large amount of available chlorine quickly, which is what clears cloudy or green water.
When to shock your pool
- When the water looks cloudy or green. See how to fix a green pool.
- After heavy rain.
- After a heavy swimmer load.
- Every 7 days in a busy pool.
How much shock to add
From the Hypo Pool Shock label: 150 g per 1 lakh litres raises chlorine by 1 ppm. A shock is 5 to 8 times that, which is 750 g to 1.2 kg per 1 lakh litres (375 to 600 g for a 50,000 litre pool). For your exact pool size, use our pool dose calculator, or see the full chlorine dose chart.
How to shock a pool
- Test the water and correct the pH first (see below).
- Dissolve the measured dose of Hypo Pool Shock in a bucket of water, then pour it around the pool with the pump running so it disperses evenly.
- Run the filter for 8 to 10 hours.
- Stay out of the pool for 4 to 6 hours, and retest before anyone swims. Free chlorine should be back between 1 and 3 ppm.
Hypo Pool Shock works with concrete, fibreglass and vinyl liner pools, as well as saltwater systems and spas.
Why pH matters before and after you shock
The ideal pH range for a chlorine pool is 7.2 to 7.6. When pH drifts too high, chlorine becomes less effective and scale forms on surfaces and equipment. When pH drops too low, the water turns corrosive and can irritate swimmers' eyes and skin. Balancing the pH is what lets your chlorine and shock treatment work as intended.
To lower high pH, use Pool Maxx pH Down: from 8.0 to 7.6 takes 1 litre per 1 lakh litres. To raise low pH, use Pool Maxx pH Up: from 7.0 to 7.6 takes 1,020 g per 1 lakh litres. With either, add no more than half the dose at a time, let the pool circulate for about 2 hours, then retest. Both work in pools, spas and saltwater systems.
If the water is still cloudy
Shocking kills algae and bacteria, but very fine particles can stay suspended and keep the water hazy. Sparkle Maxx Pool Clarifier at 150 ml per 1 lakh litres binds the fine particles together so the filter can trap them. For heavy haze, Clear Maxx Pool Flocculant clumps particles so they settle to the floor for vacuuming. More in our guide to clearing cloudy pool water.
A simple order of operations
- Balance the pH to 7.2 to 7.6 first, so the chlorine works at full strength.
- Shock the pool, run the filter 8 to 10 hours, stay out for 4 to 6 hours, then retest for 1 to 3 ppm free chlorine.
- If the water is still hazy, add a clarifier or flocculant and let the filter clear it.
Shock, pH balancers, clarifier and flocculant in one place, or everything together in the Starter Pool Care Kit.
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