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Which parameters to measure, and how often
A practical testing schedule for pools and hot tubs: what to measure at every visit, what every few visits, what once a month and what only when there is a reason.
Measure what answers a question
More tests are not always better water. Each measurement should tell you something you need to know. A practical schedule has four levels: every visit, every two or three visits, once a month and when there is a reason.
For all of it we recommend a photometer and a TDS meter. Test strips give approximate results and do not measure every value PoolHealth uses.
At every visit
- Free chlorine (FC) or bromine. It shows whether the pool or hot tub is disinfected right now.
- pH. It affects how well chlorine works in unstabilised pools. In stabilised pools its effect on disinfection is much smaller, and cyanuric acid (CYA) matters more. It affects the LSI under any conditions, and it moves with almost everything you add.
- Total alkalinity (TA). It buffers the pH, and it moves with what you do to the pool and with the water itself. It is also one of the main inputs of the LSI.
- Water temperature. It affects the LSI and how fast chemistry works, and it changes with the season and with use.
What you get back from every visit
At every visit, the app gives you figures for what to expect at the next visit. They are based on which chemicals were added and how much. They also depend on whether the pool has an automatic dosing system and how it is set up. These figures help you understand future trends.
At the next visit, compare them with what you actually measure:
- Check the doses first. Make sure the amounts you added match what was calculated.
- Check the pool volume in the pool settings.
- Then check the label of the chemical you used: its concentration and its strength, and update them in your settings if they differ.
- If the difference keeps coming back, check the pool system and write to our support.
FC new. This figure takes into account the manual chemical additions that you log into the visit data. Dosing by automated systems is not part of it: the calculation of what they add goes into the chlorine demand. If you use automation, or the pool is serviced once or twice a week, take this into account when you compare.
Every two or three visits, depending on your chemicals
If you use stabilised chlorine or calcium hypochlorite, we recommend measuring more often, every two or three visits, to see the whole picture:
- Cyanuric acid (CYA) with stabilised chlorine, because it adds CYA to the water every time you use it.
- Calcium hardness (CH) with calcium hypochlorite, because it adds calcium.
Once a month
Measure all the parameters of the LSI once a month: pH, total alkalinity (TA), calcium hardness (CH), CYA, total dissolved solids (TDS) and water temperature.
This is how PoolHealth keeps its data calibrated. The stable values between these tests are taken from the last known reading, and a monthly measurement brings them back in line with the real water, so the trends you see over a longer period stay free of errors. Read more in Why PoolHealth calculates the LSI differently.
When you need it
- Combined chlorine (CC). Measure it when free chlorine is low, or when the chlorine demand is high. Combined chlorine (CC) is chlorine that has already reacted with other compounds in the water, and it helps to explain why free chlorine does not hold.
When there is a reason
Phosphates, sulphates, iron and copper. It makes sense to measure them when:
- there is a problem that standard procedures do not solve;
- you use supplementary chemicals;
- you use an acid that contains sulphates, because sulphates can upset the balance.
You do not need to test them routinely.
Public pools
Public pools are often tested much more often than private ones, in some places several times a day, depending on the type of pool and the rules that apply. In PoolHealth you can log several visits in one day, and there is no limit on the number of logs.
At a glance
| When | What |
|---|---|
| Every visit | Free chlorine or bromine, pH, total alkalinity (TA), water temperature |
| Every 2–3 visits | CYA with stabilised chlorine; calcium hardness (CH) with calcium hypochlorite |
| Once a month | All LSI parameters: pH, TA, calcium hardness (CH), CYA, TDS, temperature |
| When needed | Combined chlorine (CC): low FC or high demand |
| When there is a reason | Phosphates, sulphates, iron, copper |
This is a general recommendation. Where the rules of your country require more frequent testing, follow them.
This article is general information, not professional advice. Always follow product labels and the rules that apply where you live.
Spotted something outdated or inaccurate? Tell us at info@pool-health.com and we will check and correct it. Last reviewed: November 2026.