Raise Hot Tub Hardness by Adding Calcium Chloride or a Water Hardness Increaser
To raise hot tub hardness, test water first (ideal range: 150-250 ppm). Add calcium chloride or a hardness increaser in small doses, circulating water for 30+ minutes between additions. Retest after 24 hours. Low hardness causes foaming, corrosion, and equipment damage, while balanced levels protect surfaces and improve water clarity.
Why Hardness Matters in Hot Tubs
- Prevents corrosion: Low calcium levels dissolve metal parts (heaters, jets, pipes).
- Reduces foaming: Soft water increases suds from oils, lotions, or detergents.
- Protects surfaces: Balanced hardness prevents etching in acrylic or fiberglass shells.
- Improves water feel: Proper levels reduce skin irritation and cloudiness.
Step-by-Step Guide to Raising Hardness
- Test current levels: Use a drop-based or digital test kit (strips are less accurate). Aim for 150-250 ppm.
- Calculate dosage:
- Check product instructions (typically 1 oz calcium chloride per 100 gallons raises hardness by ~10 ppm).
- Example: For a 400-gallon tub needing a 50 ppm increase, add 20 oz (split into 4 doses).
- Dissolve and distribute:
- Dilute powder/granules in a bucket of warm water before adding.
- Pour slowly near jets with the pump running for even distribution.
- Circulate and retest: Run the tub for 30+ minutes, then wait 24 hours before retesting.
- Adjust pH/alkalinity: Hardness changes may affect these-retest and balance if needed.
Comparison of Hardness-Increasing Methods
| Method | Cost (Per 100 Gallons) | Speed of Effect | Ease of Use | Notes |
|---|---|---|---|---|
| Calcium Chloride (Powder) | $0.50-$1.50 | 24-48 hours | Moderate | Most cost-effective; requires dissolving. Can cloud water if added too fast. |
| Liquid Hardness Increaser | $2.00-$4.00 | 12-24 hours | Easy | Pre-dissolved; less risk of clumping. Often includes stabilizers. |
| Hardness Booster Tablets | $3.00-$6.00 | 48+ hours | Very Easy | Slow-dissolving; ideal for maintenance. Higher cost per dose. |
Common Mistakes to Avoid
- Adding too much at once: Causes cloudiness or scaling. Never exceed 50 ppm per day.
- Using pool products: Pool hardness increasers may contain additives harmful to hot tubs.
- Ignoring alkalinity: Low alkalinity (<80 ppm) can prevent hardness from stabilizing.
- Skipping circulation: Uneven distribution leads to localized high/low spots.
- Not retesting: Hardness can drop again if water is diluted (rain, refills, splashing).
Maintaining Ideal Hardness Long-Term
- Test weekly: Hardness fluctuates with usage, evaporation, and chemical additions.
- Use a pre-filter: Fill tubs with pre-filtered water to reduce initial softness.
- Drain and refill: Replace water every 3-4 months to reset mineral levels.
- Monitor for signs:
- Low hardness: Foamy water, metal stains, rough surfaces.
- High hardness: Scaling, cloudiness, reduced jet flow.