From a previous post.
What you read on the internet about chloramine being a combination of chlorine and ammonia is because that is how it is manufactured in countries where it is added to the water supply as monochloramine and used as a disinfectant rather than chlorine. It is used because chlorine is a strong oxidizing agent and reacts with other compounds in the water supply to form nasties which monochloramine does not. It is used in about 25% of the USA.
It is a requirement of the Department of Health in NZ that chlorine is used as it is a better disinfectant than mono chloramine. All proteins are a double helix of phosphates with various amino acids hanging off them and all living things contain proteins. Chlorine reacts with amino acids and other nitrogen compounds to form monochloramine, then dichloramine and then trichloramine. This is called the chlorine demand when chlorinating water supplies and there will be no free available chlorine until this demand is satisfied. As the chlorine dissapates the equilibrium changes and the chloramines move back to monochloramine and this is the compound that irritates your eyes in a swimming pool and the compound that people think they are smelling as chlorine. The way to fix that problem is to add more chlorine and push the chloramines up to the trichloramine state and this is not so irritating.
It is always the case therefore that chlorinated water supplies contain chloramines and they will not be removed by storage, heating or aeration, but will be moved to the monochloramine state which is the one that is most dangerous to your fish. The only way to remove the monochloramine is with chemicals such as sodium thiosulphate which is the active ingredient in treatments available from the pet shop.
And according to Rodney Conrad:
Sodium thiosulfate instantly takes care of the chlorine in chloramine, as well as straight chlorine. The reaction to get rid of the chlorine with either chloramine or chlorine is instantaneous on mixing of the sodium thiosulfate and the chlorine or chloramine.
The reaction of sodium thiosulfate with chloramine produces ammonia. Assume you are doing a 20% water change and there is 1 PPM chloramine in the water. 1 PPM chloramine neutralized with sodium thiosulfate becomes 0.2 (20% water exchange) times 17/51.5 (molecular weight of ammonia divided by molecular weight chloramine) = 0.06 PPM ammonia level in the pond. 0.06 PPM is too low to even measure, and is safe for the fish anyway! My point is that it is perfectly safe to dechlorinate with sodium thiosulfate unless you are doing a 100 % water change and there is a huge 5 PPM chloramine concentration in the makeup water. Only then can the ammonia from the chloramine reaction with sodium thiosulfate get up to a 1.5 PPM ammonia level to give a possible real fish problem. Even then, please remember koi shipped in bags normally arrive at their destination in water that is 5 to 10 PPM ammonia level by measurement, and that is done all the time by the koi handlers without giving it a second thought. Yes, that level can do damage to the fish if you allow it to continue, no argument about that.
So all those warnings about using sodium thiosulfate to dechlorinate water containing chloramines is just so much hype from folks making a profit selling the ammonia binding products to my way of thinking about the actual technology in action.
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Alan NZKA 56