AQUATICS & RECREATION SPECIALIST GUIDE TO CALCIUM HARDNESS

Andrew
Jan 28, 2018
4 min read

Contributor: Ivana Stojkovic

Calcium hardness in commercial Swimming pools is often overlooked by experienced pool operators and not known much about by new operators.

By reviewing this information you will,

Have a basic understanding of why calcium hardness is important
Know What can happen when calcium levels are too low or too high
Know How to test for your pools calcium levels
Know how adjust to correct levels

Audience:

Property managers
Lifeguards
Aquatic Recreation managers
Apartment Maintenance
Hotel and resort maintenance

TAKE THE CALCIUM HARDNESS QUIZ HERE

What is calcium hardness

Calcium hardness in Commercial swimming pools is a measure of the mineral calcium concentration in water expressed as calcium carbonate(CaCO3).

Water with a calcium hardness of less than 200 ppm (mg/l) is described as soft water
Water with a calcium hardness above 400 ppm (mg/l) is described as hard water,

Calcium hardness is one of the most important steps of swimming pool water balance.

Understanding of water balance can be very confusing for some of pool operators.

Having a balanced swimming pool is important because,

It prevents the formation of germs and bacteria.
Incorrect water balance will affect the skin and eyes of the swimmers.
An imbalanced pool can be corrosive to the pool equipment.

Why does my swimming pool water need calcium?

Calcium is naturally found in water. Swimming pool water will look for other sources when calcium is low and ‘dump’ excess calcium when its too high.

Calcium hardness must be kept in balance, so that pool water does not become too corrosive or end up scaling the surface of your pool.
Although soft water is desirable in everyday home use, calcium hardness is necessary in pool water.
Depending on where you live and the hardness level of your local water, there can be slightly different recommendations for calcium hardness range.

What are the general accepted acceptable ranges of calcium Hardness for commercial swimming pools?

The widely Accepted range of calcium hardness in commercial swimming pools are between 200 and 400 ppm.

This can slightly fluctuate due to water temperature and other chemicals used in pool.

What happens when the calcium is low in swimming pools?

Pool water that is too soft, under 200 ppm, is known as a Corrosive water condition.

This water becomes "aggressive" and will try to increase its own hardness level by actually pulling calcium out of pool plaster.
In vinyl pools, over time, such aggressive or corrosive water will cause the pool to lose some of it's plasticity, and fail prematurely.
Fiberglass pools can become etched and lose some of the gelcoat gloss when calcium hardness levels are too low.

What happens when calcium levels are high?

Pool water that is too hard, over 400 ppm, is known as a Scaling water condition.

When the calcium levels are too high in the pool, they can precipitate, and deposit their crystals on pool surfaces, inside pipes, plug pool filters, reduce water circulation through pipes, water heaters will run less efficiently.
Calcium can make the water appear cloudy, milky, and even form precipitate flakes of calcium carbonate which are known as "Scale".

How often should calcium be tested for?

Pool water testing is important in order to achieve and maintain a sanitary and well functioning pool.

Testing pool water depends on how heavily or how lightly pool is being used along with the daily air and water temperature.
Calcium hardness should be tested once a month, but this tends to fluctuate due to local water and chemicals added to your pool.

Watch this video on how to test for calcium hardness with a TAYLOR TEST KIT

Examples of low calcium levels in a pool

Note the discoloration where the calcium has been removed from the plaster

Examples of high calcium hardness level in pools.

Note that calcium ‘spikes’ can grow on tile and pool

Note: high calcium hardness may be ONE of the reasons for cloudy water

How to increase calcium levels in pools

Keeping calcium hardness in balance is one of three important water balancing steps. The other two are pH and total alkalinity.

It’s important to make sure you have first balanced total alkalinity, then pH, and lastly calcium hardness when balancing pool water.
Test the pool for calcium hardness, and determine how many ppm you are from the midpoint of the ideal calcium hardness range.
Calcium chloride is the main chemical used to increase water hardness for pools, and it should be used per instructions on the product label.
After adding calcium chloride, you should wait about six hours for the calcium chloride to dissolve into the water, and then retest the calcium hardness level.

How to reduce calcium in pools

The easiest and most common way to reduce calcium hardness in pools is just to replace pool hard water with fresh water.

“THE SOLUTION TO POLLUTION IS DILUTION”

The first step is to test pool water for calcium hardness level. This test will determine how much water needs to be removed from the pool.
If the hardness is over the ideal calcium hardness range (400 ppm), it must be drained about one-fourth of pool water to bring the level down. This can be very expensive.
Drain a portion of swimming pool water, and refill that with fresh water.
You should wait about six hours, and then retest pool water for calcium hardness.

Another way to reduce pool hardness is using additives called flocculants. There are a few products designed for pool use, but the success of the product depends on specific water conditions of the swimming pool.

Also you can bring pool water into balance is adjusting the saturation index, which can be achieved adding an acid, such as muriatic acid or dry acid (sodium bisulfate).

How calcium levels affect other pool chemicals

Water Balance is the relationship of the different measurements of chemicals combined in the pool water.