Calcium Hardness in Pools: How to Keep Things Balanced


It corrodes your swimming pool’s metal fittings. It leaves ugly rust stains and scaly white buildup on your formerly pristine pool surfaces. It eats away at fittings and creates tiny pinhole leaks in critical pool equipment.

It’s calcium. Or calcium carbonate, if you want to be scientific about it. But whatever you call it, this naturally occurring chemical compound can be the source of common swimming pool maintenance headaches. The good news is that, with a good pool maintenance routine, you can keep your water balanced and keep pool calcium in check (and you can kiss the flakes, stains, and leaks goodbye).

Causes of Excess Pool Calcium

Excess calcium in your swimming pool is typically the result of a bigger issue with the chemicals in your pool water. As most pool owners can tell you, when it comes to water, balance is, well everything: If your pool water’s pH is off-kilter, or if your total alkalinity is too high or too low, you’ll likely end up battling algae, cloudy water, and, of course, calcium deposits.

Of course, chemical imbalances aren’t the only cause of excess calcium. Water temperature is also a contributing factor: As water temperature rises, calcium becomes more likely to precipitate out of solution. Calcium is actually more soluble in cold water, which is why scaling of heater equipment is so common.

Moderation is Key

With all of the difficulties calcium can cause, your first instinct might be to try and remove it completely – but that would be a mistake. While high calcium levels can lead to cloudy water and scale, low levels of calcium aren’t any better.

Here’s why: Water naturally wants to be balanced – and if your swimming pool water doesn’t have enough calcium, the water will actually try to balance itself out by drawing calcium from, say, your plaster pool walls in order to satisfy its need for the mineral. If you’ve got a vinyl or fiberglass pool, the water will attack metal fittings and heat exchangers, causing corrosion that can destroy the fittings and cause pinhole leaks (plus, it’ll leave telltale stains on your pool surfaces).

In other words, when it comes to your swimming pool’s calcium levels, the “Goldilocks” approach is best: Not too much, not too little. You want it to be just right.

Maintaining the Ideal Calcium Content

Like pH and alkalinity levels, calcium content is all about finding the right balance. Water should have a calcium content in the range of 100-400 parts per million.

Know the Lingo: Parts Per Million

Parts per million – often abbreviated as PPM – is a unit of measurement that tells you how much of a particular substance – such as a chemical or mineral -- is present in water.

How to Raise Hardness in a Pool

If your swimming pool doesn’t have enough calcium, you can add a pool water hardness increaser to the water easily raises calcium levels. You can buy a bucket of granular hardness increaser at just about any swimming pool retailer.

How to Lower Hardness in a Pool

If you’re dealing with too much calcium in a pool, you can try adding a sequestering agent, which is a chemical treatment that fights the effects of high metal and calcium content in swimming pool water (as an added bonus, it also fights stains). If you routinely struggle with high calcium levels or if you live in a place where hard water is an issue, you should make a sequestering agent part of your regular chemical maintenance program.

Of course, when dealing with any swimming pool issue – from calcium problems to questions about routine maintenance -- your local pool professional is a great resource. They can prescribe what is best for your pool to take care of and prevent any problem that can arise.

Calcium FAQs

Q: What is calcium hardness?

A: Calcium is always present in your pool. Hardness is the measure of how much calcium (or calcium carbonate) is present in your swimming pool water. Excessive calcium in a pool is typically the result of an imbalance in your pool water, and it can result in white, scaly buildup.

Q: What causes excess calcium in a swimming pool?

A: In most cases, excess calcium happens when your pool water is not properly balanced. Common culprits are high pH, fluctuating temperatures, and evaporation.

Q: How do I find out the calcium content in my swimming pool water?

A: Most swimming pool testing kits measure calcium along with other important levels such as chlorine, pH and alkalinity. If you’re new to pool chemistry, you might want to start with easy-to-use test strips.

Q: How do you remove calcium buildup from a swimming pool?

A: For a plaster swimming pool surface, a pumice stone works wonders. For tile, however, you should use something less abrasive. Try vinegar and a scrub brush.