How To Test Calcium Hardness In Your Pool

Written by Michael Dean
April 27, 2023

testing calcium hardness

Maintaining and testing your pool water is essential for ensuring the water remains clean and safe. There are many different chemicals in a pool, but one that many pool owners often forget to test for is calcium hardness.

If you need to brush up on your know-how on testing for calcium hardness in your pools, this article will cover the basics of ideal calcium levels and how to test for it using either test strips or a liquid drop test, so let’s dive in!

Main Takeaways

  • If the calcium levels in the pool are too low, water becomes corrosive and causes damage to the pool’s surfaces and equipment.
  • If the levels are too high, you’re looking at damage to your piping, equipment, and scaling on the surfaces of your pool tiles and fixtures.
  • To test calcium hardness levels, you’ll need a test strip or a liquid drop test kit.
  • Balancing calcium levels involves partially draining and refilling water or a calcium hardness increaser, depending on whether you need to lower or raise the levels.

What’s the Ideal Calcium Hardness Level?

I recommend maintaining calcium levels between 175 and 400 parts per million (ppm). However, this depends on the type of pool you have.

For instance, with vinyl liner and fiberglass pools, the ideal calcium levels fall between 175 and 225 ppm, while concrete and plaster pools are in a higher range, between 200 and 300 ppm. And for a saltwater pool, the ideal calcium hardness levels are between 200 and 400 ppm.

If the calcium levels in the pool are too low, the water will become corrosive (acidic) and cause pitting or scarring on the pool’s surfaces and equipment. On the other hand, if the calcium levels are too high, you’re looking at scale buildup in your pipes (which means a reduced flow of water and stress on piping), cloudy water, and scale deposits on the pool tiles, fixtures, and equipment.

It’s important to monitor and test your calcium hardness because low or high levels can harm your pool. You’ll need a test strip or a liquid drop test kit to do so.

Should You Use Test Strips or Liquid Drops?

Testing the calcium hardness using pool strips is tricky – there aren’t any test strips that test for calcium hardness by itself – they all test for total hardness, which is a combination of calcium and magnesium. Liquid test kits are the only kind of tests that measure calcium hardness on its own.

Step-by-Step: How to Test Calcium Hardness In Your Pool Using A Liquid Drop Test Kit

If you want a more accurate reading, you can opt for a liquid drop test kit instead of a pool test strip. Here’s a step-by-step guide on how to test calcium hardness in your pool using a liquid drop test kit.

Step One: Get a Sample

Collect a sample of elbow-deep pool water in the test cell. Your test cell should indicate how much water you need.

Step Two: Add the Reagent

Follow the manufacturer’s instructions to perform the test using the liquid drop test kit. This involves adding a specified number of drops of reagent to the pool water sample and swirling the water gently. There are two main ways to test calcium hardness with a liquid drop test kit, and the method you use will depend on the manufacturer. Make sure you follow the manufacturer’s instructions!

Method 1

The number of drops and their labeling vary according to the manufacturer, but commonly, you will need to add 20 drops of buffer reagent, followed by 5 drops of calcium indicator reagent (this turns the water pink or red), followed by a certain number of drops of hardness reagent (until the water turns solid blue). You must count how many drops it takes for the water to turn blue.

Multiply the number of hardness reagent drops by 10. This is your calcium hardness level in parts per million.

Method 2

Sometimes, you’ll simply add the specified number of drops to the tube and give it a swirl. Wait a few seconds, and the color should change, after which point you must compare the color in the tube to the color chart provided by the manufacturer.

Step Three: Record the Results

Record the results in a pool maintenance log or on a calendar to keep track of the calcium hardness levels over time.

Step-by-Step: How to Test Calcium Hardness in Your Pool Using Test Strips

Here is my step-by-step guide on how to test total hardness in your pool using test strips. Before you start, check the date on your test strips and ensure it is still valid, or you may get an inaccurate reading.

Step One: Dip the Strip

Dip the hardness test strip into the water. To get the best and most accurate sample of your pool water, dip the strip in elbow-deep water. Then, hold the test strip in the water according to the instruction on the packaging, usually just 10-15 seconds.

Step Two: Remove the Strip

Remove the test strip from the water. And take care not to shake off the excess water.

Step Three: Wait

Wait for the test strip to change color. The color of the test pad will correspond to a certain level of total hardness, which will be indicated on the test strip packaging. This usually takes roughly half a minute to develop. But again, make sure to read the manufacturer’s instructions for more detailed instructions according to the brand of test strip you have.

Step Four: Compare the Colors

Compare the color of the test pad to the color chart on the packaging to determine the level of total hardness in your pool.

Step Five: Record the Results

Record the results in a pool maintenance log or on a calendar to keep track of the total hardness levels over time.

How Often Should You Test For Calcium Hardness?

Test the calcium hardness level in your pool at least once a month, especially during the swimming season when you’re diving into the pool more frequently. But you may need to test more often if needed.

For example, if you’ve encountered high calcium levels in the past, you should test at least every two weeks. You should also test when adding new water, adjusting water chemistry, and after adding corrosive substances such as muriatic acid. Remember that regular testing can help you catch any problems early and take corrective action.

How to Balance Calcium Hardness Levels in Your Pool 

Balancing calcium hardness in your pool can seem daunting at first, but with some practice, it shouldn’t be too challenging. Use my calcium hardness calculator to help.

Lowering Calcium Hardness Levels

To rebalance your water if calcium levels are too high, drain some of the water and refill it using your local water supply. However, if the water supply in your local area contains high calcium deposits, you should instead try a flocculant.

A flocculant will cause the excess calcium to clump together, which will sink to the bottom, after which you can use your vacuum to remove the collected deposits. Remember: turn your pool filter and pump off before adding a flocculant. Also, avoid using a flocculant if you have a cartridge filter.

Your third and final option is to use muriatic acid. While this doesn’t directly lower calcium hardness levels, it will increase the level of saturation, balancing out your water.

Raising Calcium Hardness Levels

Raising calcium levels is thankfully much more straightforward than lowering them since it involves simply driving to your local pool supply store and purchasing a calcium hardness increaser. Add the increaser to your water according to the manufacturer’s instructions.

Get My Free Pool Care Checklist

Download my free, printable pool maintenance checklist to help you accomplish regular pool care tasks for any type of swimming pool.

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Have more questions about testing your calcium hardness? Let me know; always happy to help any way I can.

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