What chemicals does an inflatable hot tub need?

The short list

You do not need every product on day one, but test strips, a sanitiser and pH and alkalinity adjusters are the core. Some tubs come with a dispenser, such as Lay-Z-Spa's ChemConnect; check the manual for what may go in it.

The order after filling

Add each product separately with the pump running, and wait the time on the label before adding the next. Never mix chemicals together in a container.

1. 1

   Fill the tub to the line and start the filter pump so the water circulates.

2. 2

   Add anti-scale first if your water is hard and the label says to add it at filling.

3. 3

   Test the water with a strip.

4. 4

   Adjust total alkalinity into the range on your test kit.

5. 5

   Retest after the time on the label, then adjust pH.

6. 6

   Add sanitiser to reach the target level.

7. 7

   Fit the cover and let the tub heat, then retest before use.

Commonly quoted target ranges

Test kits and chemical makers give their own ranges, and you should use theirs. As general guidance, pH is commonly kept around 7.2 to 7.6, total alkalinity around 80 to 120 ppm and free chlorine or bromine around 3 to 5 ppm. See pH and alkalinity for what each reading means and how to read test strips for testing.

A simple weekly routine

Showering before use and keeping the cover on cut the work a lot, because lotions, sweat and leaves all use up sanitiser.

• Test before each use, or at least three times a week when the tub is running.
• Top up sanitiser after use to keep it in range.
• Adjust pH and alkalinity when they drift.
• Shock once a week or after a busy session, following the label.
• Rinse the filter every few days and replace it when worn.
• Drain, clean and refill every few weeks or months, as the manual suggests.

Chemical safety

Hot tub chemicals are strong. Read every label before use, wear gloves and eye protection when advised, and add chemicals to water, not water to chemicals. Keep products in their original containers, sealed, cool and dry, and store chlorine and acid products apart.

Note:Never mix different chemicals together. Store all products out of reach of children and pets, and follow the chemical maker's instructions for every dose.

Choosing between chlorine and bromine

Chlorine is fast acting and easy to test, and suits tubs that are drained often. Bromine is more stable in hot water and tends to smell less, but builds up more slowly. Check which your tub maker allows. Our chlorine vs bromine article explains the differences.

See our hot tub shortlist →

Doses depend on litres

Every dose on a chemical label is given per volume of water, so you need your tub's litres. Look in the manual or on the listing; for example, the Lay-Z-Spa Milan holds 916 litres and the Lay-Z-Spa 60001 holds 669 litres according to their listings. If yours does not say, measure the inner size and water depth and use the water volume calculator.

Start with slightly less than the full dose, then retest after the time on the label and top up. Small, regular doses keep the water steadier than large corrections, and they make it less likely you will overshoot and need a partial drain.

Frequently asked questions

Do I need all these chemicals for a hot tub? Test strips, a sanitiser and pH and alkalinity adjusters are the core. Shock and anti-scale are common additions.

What order do I add hot tub chemicals? Alkalinity first, then pH, then sanitiser, each separately with the pump running, as general guidance.

Can I use swimming pool chemicals in a hot tub? Use products sold for hot tubs and check the label and your manual, as doses and forms differ.

How much chemical do I add? It depends on the water litres. Use your tub's volume and the dose on the label.