What you are actually testing
A pool test is not a quality score. Each reading answers a different question: is there enough sanitiser, is the sanitiser in a form that works, will the correction hold until next week, and is the water going to eat the plaster or scale the heater. Read them as four questions and the numbers stop feeling arbitrary.
The bands this site uses come from the WHO’s recreational-water guidance, because it is public, dated and quotable: pH between 7.2 and 7.8 with chlorine, free chlorine around 1 mg/L in a well-run pool and never above 3 mg/L in public water, and cyanuric acid capped at 100 mg/L wherever stabilised tablets are used. Your local health code may be tighter. It is never looser.
Why the order matters
Correct alkalinity, then pH, then stabiliser, then chlorine. Every other order wastes chemicals. Alkalinity is the buffer that holds pH still, so adjusting pH first means adjusting it again on Friday. Stabiliser decides how much of your chlorine survives the afternoon, so dosing chlorine into an unstabilised pool at noon is pouring money into sunlight.
The one-line version
Buffer, then balance, then protect, then sanitise. Four steps, always that way round.
The seven readings
| Reading | Band | What it decides | How often |
|---|---|---|---|
| Free chlorine | 1–3 ppm | Whether anything is being killed | 2× a week |
| Combined chlorine | under 0.5 ppm | Whether you owe the pool a shock | Weekly |
| pH | 7.2–7.8 | How strong that chlorine actually is | 2× a week |
| Total alkalinity | 80–120 ppm | Whether pH stays where you put it | Monthly |
| Cyanuric acid | 30–100 ppm | How much chlorine survives daylight | Monthly |
| Calcium hardness | 200–400 ppm | Etching versus scale | Seasonally |
| Salt (salt pools) | cell’s own target | Whether the cell can make chlorine | Monthly |
Free chlorine, pH and cyanuric acid bands are WHO figures. Hardness and alkalinity bands are operating practice — they protect equipment rather than swimmers, and no health authority sets them.
Strips, drops and photometers
Test strips are fine for a mid-week glance at chlorine and pH and useless for anything you are about to dose. They read in bands, they age in the tub, and they cannot see combined chlorine at all. Anything that ends in a chemical going into the water should come off a drop kit or a photometer.
Keep reagents out of the truck cab in summer — heat kills them quietly, and a dead reagent reads low, which sends you to the shop for chlorine the pool did not need.
A routine that holds
Full panel monthly; chlorine and pH twice a week; write it down. The log is what turns a pool from a series of surprises into a pattern — a pool that eats 4 ppm of chlorine every Thursday is telling you something a single reading never will. Put the pattern on a weekly grid and the pool stops being a mystery.