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Pool Water Log: Track Chlorine, pH and Balance Week by Week
A few weeks of written-down readings tell you more about your pool than any chart.
What changed
- : First published.
Pool water log
Add a reading to start. Your log is saved in this browser only.
| Date | FC | CC | pH | TA | CH | CYA | Notes |
|---|
No readings yet.
How to use the log
- Test your water (see how to test pool water).
- Enter the date and whatever you measured. Leave boxes blank for tests you didn't do.
- Use the notes box for what you added, the weather or how many swimmers there were, for example "64 oz 10% chlorine, hot, party".
- Press Add reading. The newest reading appears at the top of the table, and the summary checks it against the CDC pH range and the chlorine-to-stabilizer rule of thumb.
The log is stored in your browser's local storage on this device. It stays when you close the page, but it disappears if you clear your browser data or switch to another phone or computer. Use Download CSV now and then to keep a copy.
What to log and how often
| Reading | How often | Why |
|---|---|---|
| Free chlorine (FC) | Every test | The main disinfection number. CDC suggests testing chlorine and pH at least twice a day for pools in use. |
| pH | Every test | Chlorine works less well as pH rises, especially above 8.0. CDC range: 7.0–7.8. |
| Combined chlorine (CC) | Weekly, or if the water smells | A rising CC means chlorine is reacting with contaminants faster than it is clearing them. |
| Total alkalinity (TA) | Weekly | Moves slowly. Explains pH drift. |
| Calcium hardness (CH) | Every few weeks | Moves slowly. Matters most for plaster pools and heaters. |
| Cyanuric acid (CYA) | Every few weeks and after rain or top-ups | Sets the chlorine level you need outdoors. |
Public pools are required in many places to keep written records of these tests, and CDC lists accurate record keeping among the steps for operating public pools and hot tubs. For a home pool, the payoff is understanding.
Reading your log
Daily chlorine loss. Test FC at the same time on two consecutive days without adding chlorine in between. The difference is your pool's daily use in ppm. A typical sunny outdoor pool might lose a few ppm a day; covered or shaded pools lose much less. Once you know the number, you can plan doses instead of reacting to low readings: with a daily loss of 3 ppm, a pool kept at 6 ppm needs about 3 ppm added each day. Use the chlorine dose calculator to turn that into an amount.
A sudden jump in chlorine use with no change in weather or swimmers often comes before visible algae. Test combined chlorine and look closely at corners and steps.
pH that climbs every week usually points to high alkalinity, new plaster, or lots of aeration from waterfalls and spa spillovers. See the balancing order guide.
CYA creeping upward over a season is the classic sign of relying on trichlor tablets or dichlor. Each ppm of chlorine from those products leaves behind cyanuric acid.
Example of a useful notes entry
Mon: FC 6.5, pH 7.6, "added 80 oz 10% chlorine at 7 pm". Tue: FC 3.5, pH 7.7, no additions, sunny. The pool used 3 ppm in a day. That is the figure to plan around.
Privacy
Nothing you type is uploaded. There is no account and no server copy. If you want to share your log with a pool professional, download the CSV and send the file yourself.
Sources
- CDC, Home Pool and Hot Tub Water Treatment and Testing
- CDC, Operating and Managing Public Pools, Hot Tubs and Splash Pads (keep records)
Checked Nov 11, 2026. Spot an error? Tell us.