Pool Chemistry Chart: Ideal Levels for Every Reading
The target range for each test reading in a home pool and hot tub, what each one does, and which calculator fixes it. Ranges come from the CDC, the CDC’s Model Aquatic Health Code and other sources listed at the bottom.
The chart
Target ranges at a glance
| Reading | Home pool target | Limits from health codes | Fix it |
|---|---|---|---|
| Free chlorine (FC) | Set by CYA, see the table below | At least 1 ppm without CYA, 2 ppm with CYA (CDC, MAHC) | Chlorine calculator |
| Combined chlorine (CC) | 0 to 0.2 ppm | Act above 0.4 ppm (MAHC) | Shock calculator |
| pH | 7.4 to 7.6 | 7.0 to 7.8 (CDC, MAHC) | pH calculator |
| Total alkalinity (TA) | 80 to 120 ppm | 60 to 180 ppm (MAHC) | Alkalinity calculator |
| Calcium hardness (CH) | 200 to 400 ppm plaster; 150 to 250 ppm vinyl or fiberglass | No more than 2,500 ppm (MAHC) | Calcium calculator |
| Stabilizer (CYA) | 30 to 50 ppm outdoors | No more than 90 ppm (MAHC) | Stabilizer calculator |
| Salt | Your cell’s range, often 2,700 to 3,400 ppm | None | Salt calculator |
| Saturation index (LSI) | −0.3 to +0.3 | None | LSI calculator |
Hot tubs
| Reading | Target | Limits |
|---|---|---|
| Free chlorine | 3 to 5 ppm | At least 3 ppm (CDC, MAHC) |
| Bromine | 4 to 6 ppm | 4 to 8 ppm in spas (MAHC) |
| pH | 7.2 to 7.6 | 7.0 to 7.8 (CDC, MAHC) |
| Total alkalinity | 80 to 120 ppm | 60 to 180 ppm (MAHC) |
| Water temperature | Your choice | No hotter than 104°F (MAHC) |
Free chlorine depends on stabilizer
Cyanuric acid (CYA) binds most of the chlorine in the water and releases it as it’s used. That protects it from sunlight, but it also means the same free chlorine reading kills germs more slowly as CYA rises. The widely used Trouble Free Pool chart sets chlorine as a share of CYA:
| CYA (ppm) | Minimum FC | Target FC | Shock FC |
|---|---|---|---|
| 0 (unstabilized) | 1 | 3 | 10 |
| 20 | 2 | 3 | 10 |
| 30 | 2 | 4 | 12 |
| 40 | 3 | 5 | 16 |
| 50 | 4 | 6 | 20 |
| 60 | 5 | 7 | 24 |
| 70 | 5 | 8 | 28 |
| 80 | 6 | 9 | 31 |
| 90 | 7 | 10 | 35 |
| 100 | 7 | 12 | 39 |
Free chlorine levels by stabilizer (CYA)
The Oregon Health Authority, which follows the CDC code for public pools, sets the ideal CYA at 30 to 50 ppm and closes a pool if the ratio of CYA to free chlorine goes above 45 to 1. Home pools aren’t bound by that, but it shows how seriously regulators take the link.
What to adjust first
- Total alkalinity, because it controls how much pH moves.
- pH, once alkalinity is in range.
- Calcium hardness, which changes slowly and matters most for plaster.
- Stabilizer, if you’re outdoors and it’s low.
- Chlorine, last, to the target for your CYA.
The pool chemical calculator does all five at once and works out each dose.
Testing tips
- The CDC recommends testing chlorine and pH at least twice a day in pools that see heavy use. For most homes, once a day in summer is a sensible minimum.
- DPD tests can bleach out above 10 ppm and read falsely low, even zero. Use an FAS-DPD test for shock levels.
- Test strips are fine for a quick look. Drop-based kits are more precise for alkalinity, calcium and CYA.
- Take samples from elbow depth, away from return jets and the skimmer.
Sources
- Home Pool and Hot Tub Water Treatment and Testing. U.S. Centers for Disease Control and Prevention (CDC), reviewed May 10, 2024.
- Model Aquatic Health Code, 5th edition (2024). CDC.
- Understanding the Chlorine/CYA Chart. Trouble Free Pool.
- Cyanuric Acid (fact sheet 6). Oregon Health Authority.
- Understanding LSI: The Langelier Saturation Index. Orenda Technologies.
- How much salt does the system require?. Hayward (Aqua Rite salt chlorinators).
Reviewed November 7, 2026.