Test results in, exact spa doses out — chlorine or bromine.
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.
How this is worked out
A hot tub holds a few hundred gallons, so doses are small — often a spoonful. We work out the exact amount for your tub and, where a spoon is the right tool, say it in teaspoons too.
Hot water, jets and bathers use up sanitizer fast, so the good ranges for a tub are different from a pool: chlorine 3–5 ppm, bromine 4–6 ppm, pH 7.4–7.8.
The product label always wins — if it says something different, follow the label.
Questions
How do I raise bromine?
Add chlorine. In a bromine tub, chlorine turns the bromide already in the water back into working bromine — that is why the answer names a chlorine product.
How often should I test my hot tub?
Two or three times a week, and before a soak after it has sat unused.