Hot Tub Chemical Calculator
Enter your hot tub's gallons and current/target sanitizer level — we'll give you the chlorine dose in teaspoons, or bromine guidance if that's what you use.
Dose
Safety first
- Never mix chemicals together.
- Always add the chemical to the water — never water to the chemical.
- Wear gloves and eye protection when handling pool/spa chemicals.
- Keep chemicals out of reach of children and pets.
- Always follow the product label — it overrides any guidance here.
Chlorine vs. bromine in a hot tub
Chlorine (as dichlor or liquid) kills bacteria and algae fast and is inexpensive, but dichlor adds CYA with every dose and can smell stronger at high doses. Bromine stays effective at hot-tub temperatures for longer between doses, has a milder smell, and tolerates higher pH better — but it costs more and reacts more slowly, so it's a worse choice if you need to clear a problem fast.
Maintaining bromine
Most bromine systems use a floating feeder or in-line feeder loaded with slow-dissolving tablets — you're not usually hand-dosing bromine the way you would chlorine. Check the feeder's flow setting weekly against your test reading, aiming for 3-5 ppm. If you're starting a tub from scratch, the initial "bromine bank" is built with sodium bromide activated by an oxidizer (follow your product's label for that one-time step), after which the feeder takes over for day-to-day maintenance.
Ideal ranges
Chlorine FC: 3-5 ppm. Bromine: 3-5 ppm. pH: 7.2-7.8. TA: 60-80 ppm (varies by brand).
When to shock
Shock weekly, or any time the water looks cloudy, smells stronger than usual, or right after a session with several bathers. A non-chlorine shock (potassium monopersulfate) oxidizes contaminants without spiking FC, which is gentler for frequent use than repeatedly over-dosing chlorine or bromine.
After dosing
Add the chemical with the jets running and the cover open for 15-20 minutes to mix it through the water and let any fumes clear. Re-test after 30 minutes before getting back in.
Frequently asked questions
Chlorine or bromine — which should I use in my hot tub?
Both work. Bromine is popular in hot tubs because it stays more stable at high temperatures and doesn't smell as strong, but it takes longer to kill contaminants and costs more. Chlorine acts faster, is cheaper, and is what most people already have from their pool.
Why are hot tub doses so small?
Hot tubs hold a few hundred gallons instead of thousands, so the same ppm change needs far less product. We give results in teaspoons/tablespoons since that's what most people have on hand for a tub this size.
How often should I test my hot tub water?
2-3 times per week, plus right before and after heavy use — hot tubs load up with bather waste fast relative to their volume.
Does CYA matter in a hot tub?
Only if you're using chlorine and the tub sits in direct sunlight uncovered. Most covered or indoor hot tubs need little to no CYA, and dichlor adds it with every dose — see the warning above if you use dichlor regularly.
Why doesn't this calculator give me a bromine dose in teaspoons?
Bromine in a hot tub usually comes from a floating feeder or bromine tablets, not a one-time granular dose — the feeder maintains the level between tests. Building an initial "bromine bank" uses sodium bromide, which reacts with an oxidizer rather than dosing by a simple ppm formula, so we give guidance instead of a number we can't validate.
When should I shock my hot tub?
Weekly, or anytime the water looks cloudy, smells strong, or after a session with several people. A non-chlorine (potassium monopersulfate) shock won't spike FC and is gentler on covers and skin for frequent use.