Calcium Chloride

- is a salt of Calcium and Chlorine  - chemical formula CaCl², used in pools and spas to increase Calcium Hardness. It has lots of uses in industry: - from accelerating cement set times, drying gases, paper production, food preparation and many more.

Keeping Calcium Hardness (CH) level under control in your pool is vital. Low CH will degrade the plaster finish or the grout of a tiled pool, and high CH can cause cloudiness of the water and the formation of lime-scale. The ideal CH range is 250 - 350 parts-per-million (ppm) but 100 - 500 ppm is acceptable

Newly-filled pools in areas with soft water or pools filled with rainwater may have a low CH, but this can be remedied inexpensively by adding Calcium Chloride Flakes

Calcium Hardness rises over time as water is evaporated from the pool and fresh water is used to top the pool up. The fresh water will contain some dissolved calcium, which remains in the pool when more water evaporates. So the CH reading rises inexorably over the years. Therefore, it makes sense to keep CH at the lower end of the acceptable scale for as long as possible, to delay the time when you will have to replace some of the pool water to REDUCE it.

Testing and dosage calculation

Use a Calcium Hardness test kit to determine the CH level in your pool. Test at the deep end of the pool and, if necessary, add Calcium Chloride at a rate of 2oz per 1,000 US gallons of water or (130g per 10m³) to increase Calcium Hardness by 10ppm

Add CaCl² in three separate doses; one-third of the total each time

Example, if your pool is 40m², and the CH is 100ppm when you test it, and you want to raise it by 150ppm to end up with a reading of 250ppm: -  Add a total of 130g x 4  x 15 = 7.8 Kg. 7.8 Kg divided by 3 = 2.6 Kg

Apply the first dose of 2.6 Kg, following the directions below. When it's dissolved and diluted, test again. Adjust the second dose as appropriate and test again after that.


Dissolve CaCl² in a plastic bucket of pool water. DO NOT add it directly to the pool as doing so can cause lime-scale to form a the point of contact where the un-dissolved chemical rests on the bottom of the pool

Never apply Calcium Chloride directly into the skimmer as this chemical produces considerable heat by hydrolysis and could damage the pump and/or filter.

Add it by pouring it around the pool with the pump on and allow time for it to dilute thoroughly - roughly 4-8 hours. Re-test the water after this time and add more Calcium Chloride if required


Serious Safety Issues  

Ingestion/inhalation - CaCl² can cause painful burns in the mouth, nose and throat if ingested or inhaled, as well as provoking severe coughing. Be careful not to inhale dust as this can burn the lungs.

If vomiting occurs consult a doctor

Contact - Calcium Chloride can also burn the skin on contact, especially if the skin is wet, due to hydrolysis (the chemical reaction between a chemical and water). Remove any visible traces of the chemical from the skin and irrigate the affected areas with warm water for 15 minutes. Seek medical attention if the burns are severe

Storage - keep containers tightly closed (and correctly labelled) in a cool, DRY place.

Keep all pool chemicals out of reach of children and pets to avoid accidents


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Ken Walker - MyPoolGuru©