What is Calcium Hardness in Pool Water?

Maintaining pool water can seem like somewhat of a science, and Google search results seem to contradict one another. Calcium hardness of pool water is a perfect example, causing mass confusion. I took it upon myself to ask around, and do A LOT of research to get to the bottom of the question – What is calcium hardness in pool water?

Calcium Hardness is the amount of dissolved calcium and magnesium that is in the water. Water with high levels of calcium is referred to as hard and water with low levels of calcium is referred to as soft. Calcium content is unavoidable when you fill your pool with well or borehole water.

Pool water with high or low calcium hardness is harmless to swimmers but might be damaging to your pool itself. You will need to know how to test for calcium hardness, how high and low calcium hardness can affect your pool, and how to treat high and low calcium hardness. Read on as I explain.

How Do I Test My Pools Calcium Hardness

You can use a test kit to determine your water hardness. I recommend the Aquacheck 7 test strips. These are 7 in 1 test strips that test Total Chlorine, Free Chlorine, Total Bromine, pH, Total Alkalinity, Cyanuric Acid as well as Calcium Hardness.

You can also use a chemical test kit, but these are time-consuming and complicated.

The ideal level of calcium hardness is 150 to 400 ppm.

What If My Pools Calcium Hardness is too High?

If you have hard water in your pool, there is very little you can do to lower the calcium levels.

High calcium is not a serious concern, it is harmless to humans. However, there are some things to keep an eye out for, if your pool’s water is hard.

The only way to truly lower calcium hardness substantially is to dilute it.

Pool flocculant can help to lower calcium hardness slightly. It does this by causing the calcium to bind and cause them to clump up and collect on the pool floor. You can manually vacuum them up. Be sure to turn the pump to “waste” so that these calcium clumps don’t end up in your filter.

Water softener doesn’t lower the calcium levels, it simply replaces the calcium with sodium.

High calcium hardness will cause scaling along the water as the water evaporates. This is unsightly and over time, can grow large enough to become jagged and sharp. Sharp enough to cause cuts and grazes.

High calcium hardness can also cause mineral deposits that look like little growths, usually on plaster pools. They resemble small coral, except these are formed out of calcium. These growths can get sharp and will cut feet and hands. If you notice these forming, you should sand them down with some wet sandpaper to remove the hazard.

Avoid using calcium-based products in your pool. Some pool shock products are calcium-based as well as some granular chlorines.

What If My Pools Calcium Hardness is too Low?

Water needs to have a certain amount of minerals in it to be stable, and so if the water does not have enough calcium in it, it will start to absorb calcium from the lining of your pool as well as tile grout. This over time can damage the pool surface.

If your calcium is extremely low, you will want to raise it with calcium chloride. You must do this very slowly though, because if you add too much, it is nearly impossible to undo.

Add small amounts, wait six hours and then test before adding more. Do this until you have reached the correct calcium hardness level. Also, be sure to follow the instructions on the label very carefully.


Calcium hardness in pool water is nothing but the amount of dissolved calcium in your water. Water with high levels of calcium is called hard water and water with low calcium levels is called soft water.

Both hard and soft water can damage the pool lining and equipment, however, neither is harmful to swimmers.

Hard water can cause scaling along the water line caused by calcium deposits as the surface water evaporates. Hard water can also cause the formation of calcium formations under the water, similar to coral.

These deposits and formations can be removed with chemicals or sanded down as needed. I recommend you do that because these deposits can form sharp edges and can be a hazard to your swimmers.

There is very little you can do to lower calcium levels in your pool water other than replacing or diluting the water.

A flocculant can be used to slightly lower the calcium hardness, this causes the calcium to bind and clump, falling to the floor so that you can vacuum them out.

Water softener does not remove calcium from your pool water.

Pool water from wells and boreholes almost always have high calcium levels, however, you can prevent making it worse by avoiding calcium-based chemicals, read the labels carefully.

Low pool calcium levels can damage pool lining and tile grout.

To fix this, you need to carefully add calcium to your pool water. Do not overdo it because adding too much is difficult to undo.

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