How to add chemicals to a hot tub, step by step

Before you start

If you are new to water care, start with our guide to what chemicals a hot tub needs.

• Test the water with strips or a test kit so you know what needs adjusting.
• Know your water volume in litres; see our water volume calculator.
• Read each product's label for the dose and waiting time.
• Have the pump or bubbles ready to circulate the water.
• Keep children and pets away while you dose.

The order to add chemicals

Add only one product at a time, and let it circulate before adding the next.

1. 1

   Total alkalinity first, as it buffers pH and makes it easier to hold steady.

2. 2

   pH next, using pH plus or pH minus as the test shows.

3. 3

   Sanitiser (chlorine or bromine) once pH is in range, as it works best at the right pH.

4. 4

   Shock after heavy use or as part of your weekly routine, as the label directs.

5. 5

   Optional extras such as scale or foam treatments last, only if needed.

How to add each product

Open the cover and run the filter pump or bubbles so the water moves. Measure the dose carefully. Many granular products can be sprinkled slowly over the moving water; some labels say to pre-dissolve them in a bucket of tub water first. Liquids are usually poured slowly near the water flow.

Never drop tablets or undissolved granules straight onto the floor of an inflatable tub, as concentrated chemical can damage the liner. Use a floating dispenser for tablets.

Note:Add chemicals to water, never water to chemicals. Never mix products together outside the tub. Wear gloves and eye protection if the label advises, and store chemicals in their original containers out of reach of children.

How long to wait

Leave the cover open for a short while after dosing, especially after shock, so vapour can escape and does not wear the underside of the cover.

Does temperature matter?

You can add chemicals at your normal soaking temperature. Warm water and circulation help products dissolve and mix. After a refill, many owners balance the water while it heats and add sanitiser once it is circulating. Avoid adding chemicals while anyone is in the tub.

If the heater is off for a long period, sanitiser still needs keeping in range. See should you leave a hot tub on all the time.

Keeping it simple

Most problems come from adding too much at once or several products together. Small, measured doses with a retest in between are easier to manage. Write down what you add and the results, so you learn how your tub behaves. If chlorine goes too high, see how to lower chlorine.

A tub with a good cover and filter makes water care easier. Our best inflatable hot tubs guide compares models.

Compare inflatable hot tubs →

A sample weekly routine

Test the water two or three times a week and before each soak. Adjust pH if needed, then top up sanitiser to the range on the label. Once a week, or after a busy session, add a shock dose as directed and leave the cover open while it works. Rinse the filter every few days.

This simple pattern keeps most inflatable tubs clear and comfortable. If you find you are correcting the same problem every time, look at the cause, such as hard water, a tired filter or very heavy use, rather than adding more chemicals.

Frequently asked questions

Should the pump be on when adding chemicals? Yes. Run the filter pump or bubbles so the product mixes evenly and does not sit in one spot.

Can I add chlorine and pH minus at the same time? No. Add one product, let it circulate and retest before adding the next.

How soon can I get in after adding chemicals? When sanitiser and pH have returned to their normal ranges. Follow the waiting time on the label.

Do I add chemicals before or after heating? Either works. Many owners balance the water while it heats, then add sanitiser once it is circulating.