Hot tubs and spas
Small water,
exact doses.
A hot tub holds a few hundred gallons, so a pool scoop is always too much. Put in your bromine or chlorine reading and get the dose in ounces and millilitres, not scoops, then a record of every soak and test.
Free for one hot tub. No card.
Two ways to sanitize
Bromine or chlorine, with the right numbers for each.
The targets change with the sanitizer. These are the ranges Pool Almanac uses for an acrylic hot tub, straight from its chemistry engine.
Bromine
Steady in hot water and forgiving between soaks. Usually fed from a floater or feeder.
- Bromine
- 4 to 6 ppm
- pH
- 7.2 to 7.8
- Alkalinity
- 50 to 90 ppm
- Calcium
- 100 to 250 ppm
- Stabilizer (CYA)
- Not used: it doesn't protect bromine
Chlorine
Cheaper and quick to adjust. Shock level at the target CYA: 12 ppm.
- Free chlorine
- 4 to 6 ppm
- pH
- 7.2 to 7.8
- Alkalinity
- 50 to 90 ppm
- Calcium
- 100 to 250 ppm
- Stabilizer (CYA)
- 20 to 40 ppm
Ounces, not cups
Raising chlorine by 3 ppm after a soak.
| Hot tub | 10% liquid chlorine | Dichlor 56% |
|---|---|---|
| 300 gal (1,150 L) | 1 fl oz | ¼ oz |
| 400 gal (1,500 L) | 1½ fl oz | ¼ oz |
| 500 gal (1,900 L) | 2 fl oz | ¼ oz |
From the same engine as the app. Dichlor adds stabilizer with each dose, so once CYA reaches its target, switch to liquid chlorine.
A routine that fits a hot tub.
Heat and bathers use up sanitizer fast, so small, frequent doses beat big weekly ones.
1
Before you soak
Test sanitizer and pH. Logging it takes under 30 seconds, and the app keeps every reading.
2
After you soak
Top the sanitizer back up to the middle of its range. The dose is sized for your tub's volume.
3
Every week
Check alkalinity and calcium, and clean the filter as the maker recommends.
4
Before it gets away from you
Reminders prompt the next test, and a rising or falling trend shows up before the water turns.
Hot tub questions.
Bromine or chlorine for a hot tub?
Both work. Bromine holds up better in hot water and is easy with a floater; it can't be stabilized, so it's used without CYA. Chlorine is cheaper and quick to adjust, and most people use dichlor granules at first, then switch to liquid chlorine once CYA reaches its target.
How much chlorine do I add after using the hot tub?
Enough to bring free chlorine back to the middle of its target range. In a 400-gallon tub, raising chlorine by 3 ppm takes ¼ oz of dichlor or 1½ fl oz of 10% liquid chlorine. The water check gives the exact amount for your reading.
Can I use the app for a pool and a hot tub?
Yes. The free plan covers one body of water; Premium covers every pool and hot tub you look after, each with its own targets and doses.
What temperature should a hot tub be?
No hotter than 104 °F (40 °C). Pool Almanac flags a reading above that as urgent.
Why do hot tubs need such small doses?
A hot tub holds a few hundred gallons against a pool's tens of thousands, so the same change in ppm takes a fraction of the product. Pool-sized scoops overshoot fast, which is why doses here come in tablespoons and fluid ounces.
Have a pool too?
The same app handles both, each with its own targets.