Support answer · Calcium
Do pools and spas use the same calcium hardness increaser?
Short answer: Yes, pools and spas both use calcium chloride, but dosing, package sizes, and target calcium hardness levels differ.
Based on Maytronics support, updated 2026-08-11, rewritten by Poolbots' pool experts.
The answer
What to know.
Yes. Calcium hardness increasers for pools and spas contain the same active ingredient: calcium chloride (CaCl₂). That stays the same whether the package is labeled for a pool or a spa.
Spas contain much less water than pools. That makes package size and dosing important differences when choosing a product.
Pool and spa comparison
| Detail | Pools | Spas |
|---|---|---|
| Active ingredient | Calcium chloride | Calcium chloride |
| Typical packaging | Large bags, 4 lbs to 50 lbs | Small bottles, 1 lb to 2 lbs |
| Target calcium hardness | 200 to 400 ppm | 150 to 250 ppm |
Important dosing differences
- Do not apply a pool-sized dose to a spa. Directions on pool bags usually calculate the dose for 10,000 gallons. A typical hot tub contains only 300 to 500 gallons.
- Small amounts make a difference in a hot tub. As a rule of thumb, one level tablespoon of granular calcium chloride raises calcium hardness by about 10 ppm in a standard 250-to-300-gallon hot tub.
- Choose a product labeled for your pool or spa. Buying a product intended for each is the better choice than sharing one product between both.
Source: Maytronics support. Same steps and facts, rewritten for clarity; the videos and illustrations are Maytronics' own.
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