Quick answer
A commercial hot tub log records spa water tests several times a day — typically time, free chlorine or bromine, pH and temperature — because spas have far higher bather loads per gallon than pools. Under the CDC MAHC, spas need at least 3.0 ppm free chlorine (4.0 ppm bromine), pH 7.0–7.8 and a maximum water temperature of 104°F.
- Spa free chlorine minimum: 3.0 ppm (MAHC); bromine 4.0 ppm.
- Maximum spa temperature: 104°F (40°C).
- Many codes require four or more tests per day for spas.
- Log drains and refills — small spas need frequent water replacement.
Why spas need their own log
A 600-gallon spa with eight bathers carries a contaminant load comparable to a large pool with hundreds of swimmers. Hot water accelerates chlorine loss and bacterial growth, so spa readings drift fast. That is why codes set higher disinfectant minimums and more frequent testing for spas, and why a single-line-per-day pool log does not work for them.
| Parameter | Spa limit (CDC MAHC) | Pool limit (CDC MAHC) |
|---|---|---|
| Free chlorine | 3.0 – 10.0 ppm | 1.0 – 10.0 ppm (2.0 with CYA) |
| Bromine | 4.0 – 8.0 ppm | 3.0 – 8.0 ppm |
| pH | 7.0 – 7.8 | 7.0 – 7.8 |
| Combined chlorine | < 0.4 ppm | < 0.4 ppm |
| Temperature | ≤ 104°F | — |
What to record on a hot tub log
- Each test: time, FC (or bromine), pH and water temperature.
- Daily: combined chlorine, total alkalinity, whether the drain is visible, and the operator’s initials.
- Water replacement: date of each drain-and-refill (many codes set a schedule based on volume and bather load).
- Actions: shock treatments, closures, and chemical additions.
When to close a commercial spa
- Free chlorine below the minimum (3.0 ppm under MAHC) or above 10 ppm.
- pH below 6.5 or above 8.0 (MAHC imminent-health-hazard thresholds).
- Water temperature above 104°F.
- Main drain or suction outlet cover missing, broken or not visible.
- Any diarrheal fecal incident — see the fecal incident response log.
Frequently asked questions
How often should a commercial hot tub be tested?
Before opening and several times while open. Many state codes require at least four tests per day for spas, and the MAHC requires testing before opening and at least every four hours when an automated controller is used.
What chlorine level should a commercial spa have?
At least 3.0 ppm free chlorine under the CDC MAHC (4.0 ppm if using bromine), and no more than 10 ppm while bathers are present.
What is the maximum temperature for a public hot tub?
104°F (40°C) under the MAHC and most state codes.
Can I use the same log for my pool and spa?
Use separate logs. Each body of water must have its own records, and spas need more tests per day than pools. The free Commercial Pool Log includes a dedicated spa page.
This page is an educational summary, not legal advice. Pool and spa codes differ by state and county and change over time — always confirm requirements with the health department that inspects your facility.