Lowering Calcium Hardness In A Swimming Pool – Is It Possible?

by T. Duff on April 22, 2009

Can one really reduce calcium levels in their pool water? 

It’s a good question and there’s quite a bit of debate in the industry whether chelating or sequestering agents really work…

Let’s see if we can break it down in further detail.

First let’s identity what calcium hardness really means.

Total hardness in a pool is essentially a total measurement of all the dissolved minerals such as calcium, magnesium and sodium. It is possible to have other minerals enter the water, but for the sake of simplicity, I’ll keep it at the most common.

Most in the pool industry use calcium hardness as a reference in pool water chemistry.

When calcium hardness reaches anything over about 400 ppm, bad things can take place.  This is when water can become aggressive or nonreactive, excessive scaling can take place not only on the tile line, but it can also cause issues in plumbing and equipment as well.

So, the best solution is to keep it between 200 and 400 ppm. On the low side, erosion can take place with plaster, grout, it can cause rust as well.

If the range here isn’t dialed in appropriately unpleasant things take place.

There are 2 primary causes of high calcium levels…

1.  Fill water – some water naturally has high amounts of calcium (make sure you’re testing if you drain/refill your pool with city or well water. )  If you’re planning on draining your pool, make sure you test your water source prior to doing so.  Some parts of the country are much worse than others.

2.  Chemicals.  Many chemicals that ones adds to their pool contain high amounts of calcium.  One very common example is calcium hypochlorite.  This is contained in most chlorine products (although you can get calcium free chlorine as well).  Certainly, this can contribute to the calcium levels in your pool.

Think of a glass of tea (bare with my lame analogy here ok?  :)

You add a pack or two of sugar or your favorite substitute and the tea absorbs it…no big deal.

What happens as you continue adding more packets…slowly, the tea can’t handle the addition.  Before too many packets, it begins building up at the bottom of the glass of tea.

Your pool is no different.

Solution Time:

There’s a couple of options to consider…

1.  I’m a big fan of draining the water every few years (if you have a vinyl pool or fiberglass, backwash it down several times to the skimmer over a few weeks to replace half or more of the water).  Every 3 years or so, can prevent this from becoming an issue.  Let’s say one spends about $125 to refill a pool.  This beats the pants off compared to what can take place if nothing is done.  If you have no calcium hardness issues, don’t drain – no sense in an unnecessary expense.  Let test results tell you what to do.

2.  There are numerous chelating or sequestering products on the market that can reduce calcium levels.  Well…sort of.  With current technology, the calcium doesn’t necessarily “remove” itself from the pool.  It essentially bonds with the chelating agent to create the desired end result.

Not all of these products are created equally.  Most pool retailers carry various “calcium reducers”.  I haven’t found them to be completely effective, but they will bring down calcium levels.

Hope this helps shedding some light on this subject.

Be well,



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