Calcium Hypochlorite is used very widely to chlorinate swimming pool water. The features, benefits and disadvantages are described below.
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Buy Calcium Hypochlorite
- Calcium Hypochlorite - Benefits
- Calcium Hypochlorite - Disadvantages
- Shock dosing
- More information about swimming pool and spa water treatment
Calcium Hypochlorite Features
Calcium Hypochlorite is unstabilised (it does not contain cyanurates) and so is more suited for use in indoor pools where chlorine loss through the effects of sunlight are much less.Calcium Hypochlorite is the preferred method of shock treatment because it is readily soluble and rapidly increases the free chlorine content of the water. Just as importantly the chlorine level drops quickly, especially in strong sunlight, to a level in which bathers can return into the water.
Calcium Hypochlorite is ideal for shock dosing as it is a strong oxidising agent. This enables it to destroy combined chlorines, the source of irritation and odour complaints.
Calcium Hypochlorite contains 65% available chlorine.
38 gm Calcium Hypochlorite will raise the free chlorine level of 25,000 lt water by 1 mg/litre (part per million).
Most commonly supplied as a granule, but can be tabletised for use with erosion feeders.
Regulatory Information Use this to check what is behind the brand name. Often you are buying a simple chemical. Look on the regulatory part of the label and most of the following should be there.
- Chemical Name (or "contains"): Calcium Hypochlorite, dry granular
- UN Number 2880
- Class 5.1 Oxidising
- EC Number 231-908-7
- CAS No. 7778-54-3 (Not obligatory in the UK)
For full information, download a safety data sheet
Unlike liquid Sodium Hypochlorite, it is in a granular form, which can be tabletised, stable on a long term basis when kept in cool dry conditions in a closed container.
Because it contains Calcium, the addition of Calcium Hypochlorite to soft pool water will add to the calcium hardness and help prevent corrosion.
Being unstabilised, it can be used where "chlorine lock" is a problem due to there being too much stabiliser (isocyanuric acid) in the water.
High chlorine loss in strong sunlight without the addition of a stabiliser.
It is alkaline causes pH to rise, and therefore water treated with it needs regular pH adjustment.Calcium Hypochlorite disadvantages
If the water is already hard, the addition of Calcium Hypochlorite may cause scaling. In this case its use should be limited to periodic shock dosing, or otherwise liquid Sodium Hypochlorite can be used.Shock dosing with Calcium Hypochlorite
Shock dosing or superchlorination is a process by which bather impurities are removed from the pool water. When chlorine combines with amines it forms chloramines. Hence, the term combined chlorine. Chloramines have little or no sanitising value. They are the cause of odour and irritation complaints. Often this is a sign that there is too little chlorine in the pool, not too much. Because it is a strong oxidising agent, Calcium Hypochlorite is good for shocking to destroy chloramines.
In the water, various reactions are slowly taking place.
Chlorine + Ammonia > Hydrochloric Acid + Monochloramine Monochloramine sanitises a little and does not irritate
Chlorine + Monochloramine > Hydrochloric Acid + Dichloramine Dichloramine irritates the eyes and nose and does not sanitise. Fortunately, it is unstable and in the presence of chlorine the chloramines breakdown to form hydrochloric acid and nitrogen. With the production of hydrochloric acid however, the pH will fall and unless corrected could lead to a situation where nitrogen trichloride is formed. This is the most irritant of all the chloramines.
When the shock dose of Calcium Hypochlorite is added to the water, the initial reaction is for the combined chlorine to rise. After this the free chlorine continues to rise but the combined chlorine does not, indicating that all the nitrogenous matter has been oxidised. This is known as breakpoint chlorination.
Usually, adding sufficient Calcium Hypochlorite to raise the free chlorine by 10 parts per million is sufficient for this. Calculate the Calcium Hypochlorite dose rate for a pool of known volume
Free chlorine is tested with DPD1 tablets, Total Chlorine is tested with DPD3 tablets. The combined chlorine value is obtained by subtracting the free chlorine value from the total chlorine value.
More information about DPD Tablets
