Cold Plunge Water Chemistry Cheat Sheet
Quick reference for residential + commercial operators · v1.0 · 2026
Target ranges & corrective actions
| Parameter | Target | Danger | If out of range |
|---|---|---|---|
| pH | 7.2 – 7.6 | <7.0 / >7.8 | Low: add sodium carbonate (pH up). High: add muriatic acid or dry acid (pH down). Adjust in small doses, wait 2 hr to retest. |
| Free Chlorine | 3 – 5 ppm | <1 ppm | Low: add liquid chlorine (sodium hypochlorite) or shock with dichlor. Verify pH first — chlorine inactive when pH off. |
| Combined Chlorine | < 0.5 ppm | >0.5 ppm | Shock to 10× combined chlorine level with dichlor or liquid chlorine. Run circulation overnight. Re-test 24 hr. |
| Alkalinity | 80 – 120 ppm | <60 / >150 | Low: add sodium bicarbonate (baking soda). High: add muriatic acid in small doses, retest. |
| Calcium Hardness | 200 – 400 ppm | <150 / >500 | Low: add calcium chloride. High: partial drain + dilute with fresh water. Don't ignore — chiller damage risk. |
| Cyanuric Acid (CYA) | 10 – 30 (indoor) 30 – 50 (outdoor) |
>80 | No additive removes CYA. Only fix: full or partial drain + refill. Stop using stabilized chlorine (dichlor/trichlor). |
| TDS (Dissolved Solids) | < 1500 ppm | >1500 | Only fix: full drain + refill. Schedule quarterly deep clean for residential, monthly for high-use commercial. |
| Water Temp | 38 – 55°F | <38 unsupervised | If drift >3°F from chiller setpoint: check condenser airflow, clean coils, schedule chiller service. |
| Chiller Delta-T | < 3°F from setpoint | >5°F | Refrigerant pressure check, condenser coil clean, compressor diagnostic. EPA 608 certified tech only. |
Testing frequency
Residential: pH + free chlorine 2-3× per week · full test weekly · drain quarterly minimum (every 90 days).
Commercial (gym/studio/spa/hotel): pH + free chlorine + temp daily, log with date/time/staff initials · full test 2× per week · drain every 30-60 days depending on bather load.
Commercial (gym/studio/spa/hotel): pH + free chlorine + temp daily, log with date/time/staff initials · full test 2× per week · drain every 30-60 days depending on bather load.
Common emergencies
Cloudy water: imbalanced chemistry (test all params), clogged filter (clean/replace), OR biofilm forming (shock + scrub).
Foul smell: usually combined chlorine >0.5 ppm. Shock + circulate overnight.
Skin irritation reported by user: stop access, test FC + pH immediately, check for over-chlorination or low pH.
Chiller not cooling: check condenser coil for debris (front-line fix in 50% of cases), then check refrigerant pressure, then schedule service.
Possible Legionella exposure (user reports respiratory illness within 10 days): Shut down access, drain + sanitize entire system, send water sample for Legionella testing, notify CDC if commercial facility.
Foul smell: usually combined chlorine >0.5 ppm. Shock + circulate overnight.
Skin irritation reported by user: stop access, test FC + pH immediately, check for over-chlorination or low pH.
Chiller not cooling: check condenser coil for debris (front-line fix in 50% of cases), then check refrigerant pressure, then schedule service.
Possible Legionella exposure (user reports respiratory illness within 10 days): Shut down access, drain + sanitize entire system, send water sample for Legionella testing, notify CDC if commercial facility.