How to shock an inflatable hot tub

What shocking does

Shock is a strong oxidiser. Added in a larger dose than everyday sanitiser, it breaks down organic waste in the water and the combined chlorine compounds, called chloramines, that form when chlorine reacts with that waste. Chloramines cause the sharp smell people blame on too much chlorine, when the real cause is too little free chlorine.

In bromine tubs, shock also reactivates bromide in the water back into active bromine. That is why bromine routines rely on regular shocking.

Chlorine and non-chlorine shock

Both types are widely used. Non-chlorine shock suits regular weekly use and tubs on bromine, while chlorine shock gives a stronger clean after heavy use or when water looks dull. Check which types your tub maker allows.

When to shock

How much shock an inflatable tub needs depends on its water volume and the product. The label gives the dose per litre or per 1,000 litres. Use your tub's litres from the manual or work them out with the water volume calculator.

• Once a week as part of a routine.
• After a busy session with several people.
• When the water smells strongly of chlorine.
• When the water looks dull or cloudy despite good readings.
• After refilling, if the label suggests it.
• After rain, leaves or debris get in.

Step by step

Shocking in the evening, after the last soak of the day, gives the product time to work overnight. Refit the cover once the label's time has passed.

1. 1

   Test the water and bring pH into range first, as shock works best when pH is balanced.

2. 2

   Run the filter pump so the water circulates; turn the bubbles off unless the label says otherwise.

3. 3

   Measure the dose for your tub's litres from the label.

4. 4

   Add it to the water as directed, never mixed with other chemicals.

5. 5

   Leave the cover off or open for the time on the label so gases can escape.

6. 6

   Keep everyone out of the tub during this time.

7. 7

   Test sanitiser before use and wait until it is back in the normal range.

Note:Wear gloves and eye protection if the label advises it. Never mix shock with other chemicals, add chemicals to water and not the other way round, and store shock dry, sealed and out of reach of children.

If shocking does not clear the water

If the water is still cloudy or smells after shocking, check the filter. A clogged filter cannot remove the particles the shock has broken down. Rinse or replace it and run the pump. If problems keep returning, the water may simply be old; a drain, clean and refill is often the quickest fix. See cloudy water and green water for checks in order.

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Shock and your tub's parts

Inflatable tubs have a vinyl or laminated liner, plastic fittings and a pump unit with a heater. Strong chemicals left undissolved on the floor can mark or weaken the liner, so pre-dissolve granules in a bucket of tub water if the label says to, and add them with the pump running so they spread quickly. Never drop shock into a floating dispenser or ChemConnect unit unless the manual says that product is suitable.

Avoid shocking just before you fit a new cover or store the tub, and do not overdose to save time. A larger dose than the label gives will not clear the water faster; it just takes longer to fall back to a safe level before you can use the tub. If you shock often and the water still struggles, look at the filter, bather load and how long the water has been in the tub.

Frequently asked questions

Do I need to shock my hot tub? Most owners do, weekly or after heavy use, to break down waste and spent sanitiser.

How much shock does an inflatable hot tub need? It depends on the product and the water litres. Follow the dose on the label for your tub's volume.

How long after shocking can I use the hot tub? Wait the time on the label and until sanitiser is back in the normal range.

Is non-chlorine shock enough? For routine weekly use it often is. Chlorine shock may be better after heavy use. Follow your manual.