Ideal pool chemical levels
| Test | Aim for | Also seen | Adjust with |
|---|---|---|---|
| Free chlorine (FC) | by CYA: at least 7.5 % of CYA, e.g. 3 ppm at 40 | CDC: at least 1 ppm, 2 ppm with CYA; industry 1-4 ppm | calculator |
| Combined chlorine (CC) | 0 ppm | any CC: shock to clear it | calculator |
| pH | 7.4-7.6 | CDC: 7.0-7.8 | calculator |
| Total alkalinity (TA) | 60-90 ppm, 80 common | industry 80-120 ppm | calculator |
| Calcium hardness (CH) | 200-400 ppm plaster, pebble, tile | vinyl and fiberglass often lower | calculator |
| Stabilizer (CYA) | 30-50 ppm chlorine pools | salt pools 60-80 ppm | calculator |
| Salt (salt pools) | 2,700-3,400 ppm | the number on your cell wins | calculator |
| Borates (optional) | 30-50 ppm | not above 50 ppm | calculator |
| Saturation index (LSI) | −0.3 to +0.3 | plaster: 0 to +0.2 | calculator |
Chlorine and pH change every day, so test those most often: CDC asks home pool owners to check them at least twice a day, more with many swimmers. Alkalinity, calcium, stabilizer and salt move slowly; test them when you open the pool, after heavy rain or a big top-up, and before you add anything. Every dose depends on your gallons; the pool gallon calculator saves them for all the other calculators.
Free chlorine by stabilizer level
| CYA (ppm) | Minimum FC | Target FC | Shock (SLAM) FC |
|---|---|---|---|
| 20 | 2 | 3-5 | 8 |
| 30 | 2 | 4-6 | 12 |
| 40 | 3 | 5-7 | 16 |
| 50 | 4 | 6-8 | 20 |
| 60 | 5 | 7-9 | 24 |
| 70 | 5 | 8-10 | 28 |
| 80 | 6 | 9-11 | 31 |
| 90 | 7 | 10-12 | 35 |
| 100 | 8 | 11-13 | 39 |
Stabilizer protects chlorine from sunlight but also holds most of it in reserve, so the more CYA in the water, the more free chlorine it takes to do the same work. That is why a single "1-4 ppm" is too low for a pool at 60 ppm CYA and more than needed at 20. The chart's rules of thumb: minimum 7.5 % of CYA, target about 11.5 %, shock 40 %. Salt cells make chlorine all day and can run at a 5 % minimum. Below the minimum, algae can start; to clear a green pool, use the pool shock calculator; for the daily dose, the liquid chlorine calculator.
Frequently asked questions
What are the ideal pool chemical levels?
For a chlorine pool: free chlorine at least 7.5 % of the stabilizer level, pH 7.4 to 7.6, total alkalinity 60 to 90 ppm, calcium hardness 200 to 400 ppm in plaster pools, stabilizer 30 to 50 ppm and combined chlorine 0. Salt pools add 2,700 to 3,400 ppm salt and run stabilizer higher, 60 to 80 ppm.
Which pool levels should I test most often?
Free chlorine and pH. They change with sun, swimmers and rain, and CDC asks home pool owners to test both at least twice a day, more when many people swim. Alkalinity, calcium, stabilizer and salt move slowly; test them at opening, after heavy rain or a big top-up, and before adding any of them.
Why does free chlorine depend on stabilizer?
Cyanuric acid shields chlorine from sunlight by binding most of it, so only a small share is active at any moment. The more CYA, the more free chlorine you need. Trouble Free Pool's rule: minimum 7.5 % of CYA, target about 11.5 %, shock 40 %: at 40 ppm CYA that is 3, 5 and 16 ppm.
Why do pool level charts disagree?
They start from different goals. Industry charts often give one free chlorine range, 1 to 4 ppm, and total alkalinity of 80 to 120 ppm. Trouble Free Pool ties chlorine to the stabilizer level and runs alkalinity lower, 60 to 90 ppm, which keeps pH from drifting up. Your equipment warranty may set its own limits.
What levels does a salt water pool need?
The salt level printed on your chlorinator, usually 2,700 to 3,400 ppm. Stabilizer runs higher than in a chlorine pool, about 60 to 80 ppm, because the cell makes chlorine all day; Trouble Free Pool allows a 5 % free chlorine minimum with a salt cell. pH tends to rise, so check it often.
Sources: Trouble Free Pool wiki, "CYA Chlorine Relationship" (FC/CYA chart, 7.5 %, 11.5 % and 40 % rules, 5 % for salt cells); Trouble Free Pool, "Pool Chemical Levels: Pool Industry vs Trouble Free Pool" (December 21, 2025: TA 60-90 vs industry 80-120, FC 1-4 generic, CYA 30-60 liquid and 60-90 salt); CDC, "Home Pool and Hot Tub Water Treatment and Testing" (May 10, 2024: FC at least 1 ppm, 2 ppm with CYA, pH 7.0-7.8, test twice a day). Salt range: chlorinator manuals (Hayward, Pentair). Read October 23, 2026.