Calcium Hardness Calculator: How Much Calcium Chloride to Add (or Water to Replace)

Maintaining your swimming pool’s calcium hardness level is important to keeping balanced water chemistry. I walk you through all the calculations below to figure out if you need to increase or decrease your calcium hardness level and how much calcium chloride to add to your swimming pool. Let’s get started.

Here are the steps you need to take:

Test Your Pool’s Calcium Hardness Level

Use a pool water testing kit to get a reading on the calcium hardness level. It should be between 200 ppm and 400 ppm. It should be on the lower end of that spectrum for vinyl liner and fiberglass pools (200-250), and the higher end for concrete pools. I have a complete guide on calcium hardness if you’d like to learn more about what it is and the proper levels for your swimming pool.

Calculate Your Pool Volume

If you don’t know how many gallons of water are in your pool, you need to calculate that before figuring out how to balance your calcium hardness level. You can use my pool volume calculator below.


Time To Do The Math

Alright, time to do the calculations to figure out what you need to do to your swimming pool to get your calcium hardness level back in the proper range. Based on the reading you took in the step above, you’ll need to do one of two things:

If your calcium hardness level is below the desired range, you’ll need to add calcium chloride or calcium chloride dihydrate. You can either add it by weight or by volume, so select your desired measurement in the calculator field below. For volume, the calculated value is measured in ounces by volume. For weight, it’s measured in ounces.

If your calcium hardness level is above the desired range, you’ll need to replace a percentage of your pool water with fresh water. The calculated value below will show a whole number (something like “48.2”), but it’s actually a percentage. So, in that example, it indicates that you need to replace 48.2% of the water.


Don’t hesitate to reach out if you have any questions about calcium hardness. I’m always here to help. For more maintenance tips, head to my guide on pool water chemistry.

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