Sodium thiosulfate (Na2S2O3), also spelled sodium thiosulphate, is a chemical and medication. As a medication it is used to treat cyanide poisoning and pityriasis versicolor.
It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system.
Sodium Thiosulphate can be used in a few different way, for example:
1. It can be used as a dechlorination agent for swimming pools and aquariums. Sodium Thiosulphate reacts with the chlorine in chlorinated water/tap water neutralising it, making the water safe. Standard tap water usually has a chlorine content of around 3-4 ppm chlorine, this level can be toxic to pond or aquarium fish, so treatment of tap water is always essentail before replacing pond or aquarium water. For dechlorination of 10 litres of standard tap water at 4ppm chlorine content, between 0.1g and 0.2g of Sodium Thiosulphate is required.
2. Sodium Thiosulphate is also used by photographers as a photographic fixer. It has a high affinity to soft metals and a solution can be used to dissolve photographic emulsions.
3. Cleaning — A mixture of 1 tsp sodium thiosulfate and ½ cup warm water is a useful recipe for cleaning Betadine or iodine spills on fabric.
4. Crystal Growing — Sodium thiosulfate readily forms colorless, monoclinic crystals.
Others: It has also been used as a treatment for cyanide posioning, during the tanning process of leather, as a supercooled solution experiment (similar to sodium acetate) and was also used for gold extraction.