For a hot tub you need a sanitizer (bromine tablets, or chlorine granules called dichlor), something to raise pH (soda ash) and to lower it (dry acid), baking soda for alkalinity, and test strips. Keep bromine at 4–6 ppm or chlorine at 3–5 ppm, pH at 7.4–7.8 and alkalinity at 50–80 ppm. Add calcium only if your water is soft.
Type your test results: what your tub needs
Chlorine
Bromine
Hot tub size
gal
Your test results
Skip any your test does not have.
Free chlorine
ppm
The chlorine that is working right now — it kills germs and algae.
pH
How acidic the water is. Right, chlorine works and eyes do not sting; wrong, it damages the pool.
Alkalinity
ppm
Total alkalinity holds pH steady, so it does not swing up and down.
Calcium
ppm
Calcium hardness. Too little eats plaster and heaters; too much leaves white scale.
Stabilizer
ppm
Cyanuric acid (CYA). It shields chlorine from the sun, so outdoor pools need some.
Type the size of your hot tub and at least one test result.
Step by step
1
Test the water two or three times a week.
2
Keep your sanitizer in range: bromine 4–6 ppm, or chlorine 3–5 ppm.
3
Fix alkalinity first (50–80 ppm), then pH (7.4–7.8).
4
Shock after heavy use, or once a week.
5
Drain, clean and refill every three to four months, and rinse the filter every few weeks.
The product label always wins — if it says something different, follow the label.
Why it happens
Hot water, bodies and jets use sanitizer up fast, and a small tub changes quickly — little and often beats a lot at once.
Questions
Bromine or chlorine for a hot tub?
Bromine holds up better in hot water and smells less; chlorine works faster and costs less. Pick one and stay with it.
Can I use pool chemicals in a hot tub?
Many are the same chemicals, but hot tub doses are tiny — use hot tub amounts. Never put trichlor pool tablets in a hot tub.
How often should I add chemicals to a hot tub?
Test two or three times a week and top up sanitizer each time. Adjust pH and alkalinity only when a test says so.