Pool water replacement can be partial (to dilute specific compounds) or complete (when water is beyond economical recovery). Hot tubs require complete water changes every 3–4 months.
Partial Drain Triggers
| Parameter | Trigger Level | Recommended Action |
|---|---|---|
| CYA | Above 80 ppm | Partial drain (25–50%) and refill |
| Calcium Hardness | Above 500 ppm | Partial drain (25–30%) and refill |
| TDS (hot tubs) | 1,500 ppm over baseline | Complete water change |
| TDS (pools) | Above 3,000 ppm (non-salt) | Partial drain (25%) and refill |
| Salt | Below 2,500 ppm or above 3,500 ppm | Add salt (low) or partial drain (high) |
| Calcium Hardness (spas) | Above 350 ppm | Partial drain or full change |
Hot Tub Water Change Schedule
| Usage Level | Recommended Change Interval |
|---|---|
| Light (1–2 soaks/week, 1–2 bathers) | Every 4 months |
| Moderate (3–5 soaks/week, 2–4 bathers) | Every 3 months |
| Heavy (daily use, 4+ bathers) | Every 6–8 weeks |
| Vacation rental (multiple guests) | Every 4–6 guest stays, or monthly |
| Always | When TDS exceeds 1,500 ppm over baseline |
Notes
- Partial drains are calculated by percentage: a 25% drain removes 25% of all dissolved compounds.
- When in doubt about hot tub water quality, a full drain is always the safest choice.
Sources:
- Pool & Hot Tub Alliance — Pool & Spa Operator Handbook, 2022