Quick answer
Commercial pools must test free chlorine (or bromine) and pH before opening every day and repeatedly while open. Under the CDC Model Aquatic Health Code, pools with automated chemical controllers test before opening and at least every four hours; pools fed manually often must test every one to two hours. Spas typically need more tests than pools. Always follow your state code.
- Before opening: every day, every pool and spa.
- MAHC with automated controller: at least every 4 hours while open.
- Manual chemical feed: many codes require every 1–2 hours.
- Alkalinity & CYA: typically weekly; calcium hardness monthly.
Testing frequency at a glance
| Situation | Free chlorine & pH | Other tests |
|---|---|---|
| Automated controller (MAHC) | Before opening + every 4 hours | CC daily; TA & CYA weekly |
| Manual / erosion feeder | Before opening + every 1–2 hours (many states) | CC daily; TA & CYA weekly |
| Spa / hot tub | Before opening + several times daily (often 4+) | Temperature every test |
| After a heavy bather load or event | Extra test immediately after | — |
| After a contamination incident | Throughout the treatment & before reopening | Record CT achieved |
Examples of state requirements
State codes range from the MAHC baseline to stricter schedules. Wisconsin ATCP 76, for example, ties testing to the pool type: whirlpools test pH and sanitizer four times a day, while standard pools test at opening and at peak use, with requirements that change when electronic monitoring is in place (see our Wisconsin pool log guide). Other states require hourly testing when there is no automatic controller.
How to prove you tested on time
- Write the actual time of each test, not "AM" / "PM".
- Make the first entry each day before the posted opening time.
- Use one line per test so the number of tests per day is obvious.
- Initial each entry so the tester can be identified.
Frequently asked questions
How often do public pools need to test chlorine?
Before opening each day and repeatedly while open. The CDC MAHC sets at least every four hours for pools with automated controllers; many state codes require every one to two hours when chemicals are fed manually.
How often should cyanuric acid be tested?
Usually weekly or monthly for outdoor pools that use stabilized chlorine or CYA. Check your code — some states cap CYA and require regular testing.
Does an automatic controller mean I do not have to test?
No. Controllers must be verified with manual tests, and the manual results go in the log.
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.