Technical info - Pure-Spa Sanitiser Tablets
These small, white tablets are based on dry chlorine donor, sodium dichloroisocyanurate (NaDCC) which is blended with effervescent components before being compressed into tablet form.  The result is a fast-dissolving, highly convenient, safer and more accurate alternative to liquid bleach.
Chlorine is regarded by many, including the Health Service and the Government, as one of the most effective disinfectants in the fight against disease. That is why it is recommended by the world's major authorities for use against HIV (AIDS) and Hepatitis B viruses and why almost all of the world's piped water supplies are treated with chlorine
Disinfecting solutions prepared from Pure-Spa Sanitising Tablets containing NaDCC are fast acting and have a complete spectrum of biocidal activity.  Bacteria, bacterial spores, algae, fungi, protozoa and viruses are all sensitive to their effects.
The problem of corrosion associated with liquid bleach has often resulted in the use of more expensive and less effective alternatives.  It has been demonstrated that chlorine solutions produced using NaDCC tablets are in general significantly less corrosive.

Labelling - Sanitiser Tablets (single pot, 30 tablets)

Contains Troclosene Sodium
1.7g NaDCC per tablet

Caution: Solution may bleach fabrics.
Harmful if swallowed.
Irritating to eyes and respiratory system.
Contact with acid liberates toxic gases.
In case of contact with eyes rinse immediately with plenty of water and seek medical advice.
Keep out of reach of children.
Keep container dry.
In case of explosion do not breathe fumes.
Warning: Do not use together with other products. May release dangerous gases (Chlorine)
Very toxic to aquatic organisms

Note:
The warnings & the hazard symbols on the pack are designed to refer to the entire pot of tablets, not neccessarily to one tablet that is dissolved in a bath full of water (approx 150L).