A De-chlorinator is a chemical used to treat chlorinated or chloraminated water. Most water sources usually have chlorine or chloramine added to it, to kill germs and other harmful organisms in the water. While chlorine poses little or no harm to human beings and most land creatures, it can harm water creatures such as fish. For this reason fish, and other water animals, keepers need to remove that chlorine and or chloramine.
Usually, very little amounts of De-Chlorinator are needed to treat water. A drop of this chemical additive, with no other 'properties', can be used to treat between 16000-20000 Litres of water. Chlorine evaporates fast, from water, once De-Chlorinator has been added to that water; stirring the water evaporates chlorine even faster. This chemical, normally, does not have side effects, but to ensure the safety of fish and other water creatures, people should ensure they do not use too much of it in small aquariums/ tanks, and that there is adequate filtration.