Replied by Ted (Bangkok, Thailand)
Dear Nina: Early gas masks in during the World War I was made of activated charcoal and they absorb toxic gas, which happens to be chlorine and mustard gas. Of course the antidote to them all is also sodium thiosulfate, the same chemicals you kill the chlorine that you buy from pet shops that sells aquarium fish tanks. They referred to as a dechlorinator and you can use it for treatment of your water as well. Most swimming pool suppliers sell sodium thiosulfate by the kilogram, but you only need a couple of drops per liter of 10% sodium thiosulfate solution to neutralize the chlorine too. Of course, simple activated charcoal will do it without that, but where I live, i always drink water with this sodium thiosulfate to detox my liver anyway and to reduce constipation.