Hot tub water chemistry has tighter acceptable ranges than pool chemistry. Test before every soak session.
Hot Tub / Spa Parameters
| Parameter | Minimum | Ideal Range | Maximum | Unit |
|---|---|---|---|---|
| Free Chlorine | 2.0 | 3–5 | 10 | ppm |
| Bromine | 3.0 | 3–6 | 8 | ppm |
| Combined Chlorine | 0 | 0 | 0.5 | ppm |
| pH | 7.2 | 7.2–7.8 | 8.0 | pH units |
| Total Alkalinity | 60 | 80–120 | 150 | ppm |
| Calcium Hardness | 100 | 150–250 | 350 | ppm |
| CYA | 0 | Not required (indoor) | 30 | ppm |
| TDS over baseline | 0 | <1,000 | 1,500 | ppm |
| Temperature | 98 | 100–104 | 104 | °F |
Notes
- CYA is not recommended for covered or indoor hot tubs — UV protection is not needed.
- Change hot tub water every 3–4 months or when TDS exceeds 1,500 ppm over baseline.
- Test before every soak — hot tub chemistry changes within hours.
Sources:
- Pool & Hot Tub Alliance — Pool & Spa Operator Handbook, 2022