Stabilised chlorine granules (Dichlor) are used very widely to chlorinate swimming pool water. The features, benefits and disadvantages are described below.

stabilized chlorine

Stabilised chlorine granules (Dichlor) features

Stabilized chlorine granules (Dichlor) dissolve in water to give not only the free chlorine (hypochlorous acid) that sanitises, but also isocyanuric acid.

Stabilised chlorine granules (Dichlor) contain 56% available chlorine.

Most commonly supplied as a granule, but can be tabletised.

Probably the most commonly used form of chlorine for smaller domestic pools.

45gm Dichlor will raise the free chlorine level of 25,000 lt water by 1 mg/litre (part per million).

Calculate the Dichlor dose rate for a pool of known volume

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"): troclosene sodium, dihydrate. This is the "official" name in the UK Approved list. It is far more commonly called sodium dichloroisocyanurate which is often shortened to dichlor.
  • UN Number 2465 refers to the anhydrous material. The hydrated material is not subject to ADR carriage conditions.
  • EC Number 613-01-7
  • CAS No. 051580-86-0 (Not obligatory in the UK)

For full information, download a safety data sheet

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

Stabilised chlorine granules (Dichlor) benefits

Unlike liquid sodium hypochlorite, it is in a granular form, and is stable on a long term basis when kept in cool dry conditions in a closed container.

Because it does not contain calcium, it can be used to sanitise hard water without increasing the calcium hardness

It is reasonably close to neutral when dissolved in water and therefore requires less pH correction than trichlor and calcium or sodium hypochlorite

The use of stabilised chlorine granules (Dichlor) adds isocyanuric acid to the pool water which resists chlorine loss from the effects of bright sunlight

Stabilised chlorine granules (Dichlor) disadvantages

Because it is a weak oxidising agent and contains stabiliser, Dichlor is not suitable for shock dosing

Excess stabiliser can build up in the water causing the chlorine to become "locked" and unavailable for sanitising. The isocyanuric acid level should be maintained between 50 to 100 mg/litre.

Shock dosing

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 much better for shocking than dichlor. More information about Calcium Hypochlorite and shock dosing

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