Pool & hot tub target levels
Typical ranges for residential pools and hot tubs, and why each one matters.
| Parameter | Chlorine pool | Salt pool | Hot tub | Too low | Too high |
|---|---|---|---|---|---|
| Free chlorine | 7.5–11.5% of CYA (e.g. 3–5 at CYA 40) | 5–7.5% of CYA (e.g. 3–5 at CYA 70) | 3–5 ppm | Algae, cloudy water, germs survive | Bleached swimwear, skin and eye irritation at extreme levels |
| Combined chlorine | 0.5 ppm or less | — | Chlorine smell, irritation: shock | ||
| pH | 7.2–7.8 | 7.2–7.8 | 7.4–7.8 | Etching, corrosion, stinging eyes | Scale, cloudy water, weaker chlorine |
| Total alkalinity | 60–120 ppm | 50–90 ppm | 50–80 ppm | pH swings | pH keeps rising |
| Calcium hardness | Plaster 250–450; vinyl/fiberglass 150–350 ppm | 100–250 ppm | Etching of plaster and grout | Scale, cloudy water | |
| Stabilizer (CYA) | 30–50 ppm (indoor 0–20) | 60–80 ppm | 0–30 ppm | Sun burns off chlorine fast | Needs much more chlorine |
| Salt | — | Per cell manual, typically 2,700–3,400 ppm | — | Low output, cell wear | Corrosion, cell errors |
Typical residential ranges; equipment and surface manufacturers may specify different values, and public pools must follow local codes. The FC/CYA ratios are a widely used rule of thumb from pool-care communities and chlorine/cyanurate chemistry.
Why stabilizer changes the chlorine target
Cyanuric acid binds most free chlorine in a reversible reservoir that protects it from UV light. Only a small unbound fraction does the fast sanitizing, and that fraction depends mostly on the ratio of FC to CYA, not on FC alone. That is why 3 ppm FC is plenty at 30 ppm CYA but too little at 80 ppm.
Not professional advice. Results are estimates for residential pools and hot tubs. Read and follow product labels: add chemicals separately, to water (never water to chemicals), with the pump running, and retest before adding more. Commercial and public pools must follow local health codes.