Hot tub chemistry chart
The ideal hot tub pH is 7.4–7.6, with 3–4 ppm free chlorine (up to the limit on your label) or 4–6 ppm bromine.
Always follow your product’s label directions. Pool and spa chlorine, bromine, shock and algaecides are EPA-registered pesticides: use products labeled for pool or spa use, and don’t swim or soak until levels are within the limit on your product’s label. If this page and a label disagree, the label wins.
On this page (8 sections)
The acceptable pH range is 7.2–7.8. Keep total alkalinity at 80–120 ppm and calcium hardness at 150–250 ppm. Hot tubs should have no stabilizer (CYA) and water no hotter than 104 °F.
The chart: every level for chlorine and bromine tubs
| Parameter | Target | Acceptable |
|---|---|---|
| Free chlorine (FC) | 3–5 ppm | at least 3 ppm (CDC) |
| Bromine | 4–6 ppm | at least 4 ppm (CDC) |
| pH | 7.4–7.6 | 7.2–7.8 |
| Total alkalinity (TA) | 80–120 ppm | 60–180 ppm |
| Calcium hardness (CH) | 150–250 ppm | 100–800 ppm |
| Stabilizer (CYA) | none | not recommended (CDC) |
| Water temperature | — | 104 °F or lower |
Sources: CDC, MAHC 2024 Annex, PHTA / ANSI-APSP-11 (via PHTA documents), Taylor. Target ranges are our choice inside the acceptable ranges; see methodology.
Download this data (CSV) · License: CC BY 4.0
"Target" is where to aim when you adjust. "Acceptable" is the wider range where you don't need to act right away. The acceptable ranges come from the CDC, its Model Aquatic Health Code (MAHC), and the industry standard for spas published by PHTA. The targets are the ideal ranges from Taylor's test kit guide, which we use as our defaults. Where the sources differ, we explain our choice on the methodology page.
What to do when a number is off:
| Reading | Too low | Too high |
|---|---|---|
| Free chlorine | Add chlorine to 3–4 ppm before soaking; doses by tub size | Cover off, jets on, wait until it is at or below your label's limit (often 4 ppm) |
| Bromine | Open floater a notch; shock to reactivate bromide | Remove floater, cover off; partial drain if urgent |
| pH | Soda ash (pH increaser), after checking alkalinity | Dry acid (pH decreaser); lower alkalinity if pH keeps rising |
| Total alkalinity | Baking soda | Acid plus aeration, in rounds |
| Calcium hardness | Calcium chloride, dissolved first | Drain part of the water and refill |
| CYA (stabilizer) | Target is zero | Only draining removes it |
| Temperature | — | Turn it down to 104 °F or lower |
pH: ideal range and what 8.0+ means
We aim for 7.4–7.6: comfortable for eyes and skin, gentle on the heater, and good for sanitizer. The CDC accepts 7.0–7.8. pH matters for sanitizer strength, and far more for chlorine than for bromine:
| pH | Chlorine (HOCl) | Bromine (HOBr) |
|---|---|---|
| 7.0 | about 70% | — |
| 7.5 | about 50% | about 94% |
| 8.0 | about 20% | about 83% |
A pH of 8.0 or more in a chlorine tub means most of your chlorine is inactive, calcium is more likely to scale on the heater and jets, and the water may haze. Most test strips and drop kits read no higher than 8.2, so "8.2" often means "8.2 or higher." Bring it down in steps. The high pH fix has a calculator and explains why pH keeps coming back. If pH reads below 7.2, see low hot tub pH.
Alkalinity or pH first?
Alkalinity first. Total alkalinity (TA) is the water's buffer: it decides how easily pH moves. If TA is out of range, any pH correction drifts back. Taylor's instructions put it plainly: "Always bring total alkalinity into range before adjusting pH."
The exception is sanitizer. If chlorine or bromine is below the minimum, fix that first because it is a health issue. Then fix TA, then pH. Our calculator follows that order. For amounts, see raising or lowering spa alkalinity.
A tip for tubs with pH that keeps climbing: aim for the lower half of the TA range (80 ppm, or even 60–80). Lower alkalinity means less carbon dioxide for the jets to drive out, so pH rises more slowly.
Calcium hardness for acrylic shells
Most hot tubs have acrylic shells, not plaster, so calcium isn't protecting a surface the way it does in a plaster pool. It still matters:
- Too low (below about 100 ppm): water is more corrosive to metal parts. Very soft water is also often blamed for foam, though we could not confirm that with a primary source. Check your manual for the manufacturer's minimum.
- Too high (well above 250 ppm with high pH and heat): white scale on the waterline, jets, and heater element.
We use 150–250 ppm as the target, the ideal range Taylor gives for spas. The industry standard allows 100–800 ppm. Calcium only goes down with fresh water, so if your tap water is hard, partial drains are the fix. In a 400-gallon tub, 22 g (0.75 oz) of 77% calcium chloride raises calcium hardness by about 10 ppm.
Check your numbers against the chart
Enter your latest test. The calculator color-codes each reading and puts the corrections in order.
Printable PDF
Print this page, or choose "Save as PDF" in your browser's print dialog. Menus and buttons don't print. Tape the chart inside the cabinet door or next to your test kit. The pool version, with stabilizer and salt, is the pool chemistry chart.
FAQ
What is the perfect pH for a hot tub?
7.4–7.6. It is comfortable, protects equipment, and keeps chlorine working. The CDC's acceptable range is 7.0–7.8.
Should you adjust alkalinity or pH first in a hot tub?
Alkalinity first. If sanitizer is below the minimum, fix sanitizer first, then alkalinity, then pH.
What should hot tub alkalinity be?
80–120 ppm as a target; 60–180 ppm is acceptable. If pH keeps rising, keep it near 80 ppm or a little lower.
Sources
- CDC, Home pool and hot tub water treatment and testing (3 ppm chlorine minimum, pH 7.0–7.8, no CYA in hot tubs): cdc.gov
- CDC, Model Aquatic Health Code 2024, Annex (spa sanitizer ranges; HOCl and HOBr by pH): cdc.gov (PDF)
- Taylor Technologies, K-1005 instruction manual (ideal ranges, alkalinity before pH): PDF
- PHTA / AQUA Tech Notes with the ANSI/APSP-11 table (spa calcium range, 104 °F): PDF
- U.S. Consumer Product Safety Commission, hot tub temperatures: cpsc.gov