Calcium hardness calculator
Calcium hardness protects plaster and equipment. Enter your current and target calcium hardness and pool volume to get the exact amount of calcium chloride to add.
How much calcium chloride to add?
About 1.2 lb of calcium chloride (77%) per 10,000 gallons raises calcium hardness by roughly 10 ppm. The calculator scales it to your volume and product strength. Pre-dissolve it in a bucket of water (it gets hot), then pour around the pool.
Why calcium hardness matters
Too low and the water gets aggressive — it etches plaster and corrodes metal to find the calcium it’s missing. Too high and it scales surfaces and clouds the water. Plaster pools want more calcium than vinyl or fiberglass.
Calcium too high?
There’s no chemical to remove calcium — lower it by partial drain-and-refill (or a softener fill). It’s a slow problem, so prevention via balanced water (LSI) is the real fix.
Ideal ranges
| Level | Target | Notes |
|---|---|---|
| Plaster / gunite | 250–450 ppm | Needs calcium |
| Vinyl / fiberglass | 175–375 ppm | |
| Hot tub / spa | 150–250 ppm |
Frequently asked questions
Does cal-hypo add calcium?
Yes — calcium hypochlorite shock adds calcium over time. If your calcium is already high, prefer liquid chlorine.
What’s LSI?
The Langelier Saturation Index combines pH, temperature, calcium, and alkalinity into one balance number. The DoseMyPool app shows it so you can keep water gentle on surfaces.
Related calculators & guides
Get exact doses, saved and on schedule
DoseMyPool remembers your pool, gives the safe order to add things, and reminds you to test — free on the App Store.