What to know.
Swimming pools and spas use the exact same chemical to increase calcium hardness.
Whether a bottle is labeled for a pool or a spa, the active ingredient is always calcium chloride (CaCl₂). However, because spas hold a much smaller volume of water than pools, there are critical differences in how you buy and dose the chemical.
Quick Comparison
| Active Ingredient | Calcium chloride | Calcium chloride |
| Packaging Sizes | Large bags (typically 4 lbs to 50 lbs) | Small bottles (typically 1 lb to 2 lbs) |
| Target Level | 200 to 400 ppm | 150 to 250 ppm |
Important Dosing Differences
- The Danger of Pool Instructions: Instructions on a pool bag are usually calculated for 10,000 gallons of water. A typical hot tub only holds 300 to 500 gallons.
- The Hot Tub Rule of Thumb: In a standard 250-to-300-gallon hot tub, just one level tablespoon of granular calcium chloride will raise the hardness level by roughly 10 ppm.
- It is best to buy products that are specific to your pool or spa, instead of using a single product for both.
Source: Maytronics support. Rewritten for clarity with the same steps; the videos and illustrations are Maytronics' own.
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