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

stabilized chlorine

Stabilised chlorine tablets (trichlor) features

Stabilized chlorine tablets (trichlor) dissolve in water to give not only the free chlorine (hypochlorous acid) that sanitises, but also isocyanuric acid which resists chlorine loss from the effects of bright sunlight.

Stabilised chlorine tablets (trichlor) contain 90% available chlorine.

Most commonly supplied as either a 20gm or 200gm tablet.

The 20gm tablet is 30mm diameter by 16mm high. The 200gm tablet is 75mm diameter by 25mm high.

Probably the most convenient form of chlorine for smaller domestic pools.

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

Being acidic, the tendency will always be to reduce pH. This may or may not be advantageous.

Calculate the trichlor 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"): trichloroisocyanuric acid. This is the "official" name in the UK Approved list. It is less commonly called trichloro-1,3,5-triazinetrion or symclosene. Trichloroisocyanuric acid is often shortened to trichlor.
  • UN Number 2468
  • EC Number 613-031-00-5
  • CAS No. 000087-90-1 (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 tablets (trichlor) benefits

Unlike liquid sodium hypochlorite, it is in a solid 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.

As it is in a tablet form, it is suitable for semiautomatic dispensing using an erosion feeder or chlorinator.

In alkaline water, the use of trichlor will decrease the necessity to adjust pH downwards.

Stabilised chlorine granules (trichlor) disadvantages

Because it is a weak oxidising agent, slow to dissolve and contains stabiliser, trichlor is not very suitable for shock dosing

In neutral water, there will be a necessity to counteract a drop in pH.

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 trichlor. More information about Calcium Hypochlorite and shock dosing

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