Hot Tub Chemicals Guide
Pick one sanitiser, keep the water in range, and test twice a day
Hot tub chemicals do four jobs: sanitise, balance, fix problems and test. This guide shows what goes on each shelf, what to aim for and how to add it safely.
Add one chemical at a time, and never mix them.
Four jobs, four shelves
Hot tub chemicals sort into four jobs: sanitise, balance, fix problems and test. The CDC advises testing pH and sanitiser levels at least twice a day.1
| Shelf | What it does | What to aim for |
|---|---|---|
| Sanitise | Keeps the water clean and kills bacteria | Chlorine 3 ppm minimum, bromine 4 ppm minimum.1 Our bromine pages aim for 3 to 5 ppm.3 |
| Balance | Keeps pH, total alkalinity and calcium hardness in range | pH 7.0 to 7.8.1 Total alkalinity 80 to 125 ppm for wood, plaster or tile tubs and 125 to 150 ppm for vinyl, painted or fibreglass tubs. Calcium hardness 150 to 200 ppm.2 |
| Fix problems | Shock, anti-foam and anti-scale | Shock daily to weekly.1 No Foam when foam appears.4 No Scale weekly.5 |
| Test | Shows what the water needs before you add anything | At least twice a day, and hourly in heavy use.1 |
Pick one sanitiser
You need one sanitiser at a time. Here is how the three compare.
| Sanitiser | How you add it | What the product page says |
|---|---|---|
| Bromine | Tablets in a floater or feeder, or granules | Gentler on skin than chlorine, with a less harsh odour and steadier levels.3 |
| Chlorine | Granules, dissolved in the water | Dissolves quickly and raises chlorine levels faster than tablets.6 |
| Oxygen | 20 g tablets in a floating dispenser, one per 1,500 litres, with the matching liquid | An alternative to chlorine or bromine as your regular sanitiser.7 |
Stay with the one you choose. Never mix chemicals together, including different types of chlorine.2 See the chlorine and bromine ranges, and our sanitiser guide for the levels.
Keep the water in balance
pH sits at 7.0 to 7.8,1 and total alkalinity helps hold it there. Our pH and total alkalinity guide covers the steps and the products.
Fix common problems
Shock
Shock lifts the water between sanitiser doses. The CDC advises a shock treatment daily to weekly, depending on use.1
Our shock guide has the steps and the dose.
Foam
Test and rebalance sanitiser and pH first. If foam remains, add no more than 20 ml of No Foam with the jets on.4
Use it as and when you notice foam.
Scale
No Scale keeps calcium in solution, which protects the heater and pipes. Add about 15 ml per 1,000 litres weekly.5
Shake the bottle first and pour it in with the pumps on.
Cloudy water
Start with a test, then follow the steps in our cloudy, foamy or green water guide.
It covers what each colour and symptom points to.
Test, then add
Test before you bathe
Read sanitiser, pH and total alkalinity with one dip of the 3-in-1 strips. See the strips.1
Add one product at a time
Add each chemical on its own, and always add chemicals to water, not water to chemicals.2
Wait for it to dissolve
Allow at least 30 minutes for the chemical to dissolve before bathing.2
Test again
Retest and adjust only what is still out of range.
Your starter shelf
One product for each job. Every one is a current Outdoor Living product, in stock now.
3-in-1 Pool and Hot Tub Test Strips
Pack of 50 · £4.99
Test. Reads sanitiser, pH and total alkalinity in one dip.
Quick answers
Open a question to read the answer.
Which sanitiser should I choose?
Choose one: chlorine, bromine or an oxygen-based sanitiser. Our bromine page describes bromine as gentler on skin than chlorine, with a less harsh odour and steadier levels. Chlorine granules dissolve quickly, and oxygen is an alternative to both.
Can I mix hot tub chemicals?
No. Add each chemical on its own, and never mix chemicals together, including different types of chlorine.
How often should I test the water?
At least twice a day, according to the CDC, and hourly when the tub is in heavy use.
What should I do about foam?
Test the sanitiser and pH first and rebalance them. If foam remains, add no more than 20 ml of No Foam with the jets on.
Where should I store hot tub chemicals?
Keep them in their original containers, out of children's reach, in a clean, cool, dry place away from the heater.
Sources
- Centers for Disease Control and Prevention, Operating and Managing Public Pools, Hot Tubs and Splash Pads (dated 10 January 2025): sanitiser minimums, pH, shock and testing
- King County, Washington, Department of Public Health, Staying Happy and Healthy in Your Spa and Hot Tub, sixth edition (undated): alkalinity and hardness ranges, chemical storage and handling
- Outdoor Living, Hot Tub Bromine Tablets product page: dosing and level (current)
- Outdoor Living, Hot Tub No Foam product page: use and dose (current)
- Outdoor Living, Hot Tub No Scale product page: use and dose (current)
- Jacuzzi, Hot Tub Chlorine Granules product page, sold by Outdoor Living: use and dose (current)
- Jacuzzi, Hot Tub Oxygen Tablets product page, sold by Outdoor Living: use and dose (current)
- Jacuzzi, Hot Tub Hardness Increaser product page, sold by Outdoor Living: calcium level (current)
Paul Margerison
Managing Director & Founder, Outdoor Living
Good water care is a short routine: test, add one thing, wait, and test again.