Sodium Thiosulphate

Water companies began adding Chloromites to tap water which is poison to fish. Sodium thiosulphate is used to get rid of Chloromites in tap water.

Sodium thiosulphate
Chloramine==Ammonia?

Use a standard sodium thiosulfate declorinator for both chlorine and chloramine. However, for chloramine use it double strength. Some (and I am being cagey here) products designated to neutralize chloramine are known by their manufacturers to be toxic to fish at concentrations higher than that recommended on the bottle. ie, you have to be fairly precise. The old standard however is very forgiving. No one advertises this as it is likely to hurt sales. Moderate plant growth will take care of any excess ammonia released by the application of sodium thiosulfate to chloramine.
Declorinators (like thiosulfate) will break the chlorine + ammonia bond and set the ammonia free (so as I am told). This replaces toxic choraimine with potentially toxic ammonia. Now, extra thiosulfate will handle the free clorine. So, that leaves the ammonia...

The concentration of the released ammonia will be related to the concentration of the original chloramine. The resultant ammonia concentration is something similar to the chloramine concentration. So, I think we are talking about 1 to 2 ppm (mg/l) of ammonia (to be diluted according to the % water change). For 50 % change you can have 1 ppm of ammonia. The amount of this that is toxic to fish will depend mostly on pH but also on temperature. (There is an equilibrium between toxic NH3 and non-toxic NH4). Worst case is high pH and high temperature. At 8.5 pH and 86 deg, 20 percent would be toxic NH3 (~ 0.2 ppm). This is a lot and roughly corresponds to lethal dose for 1-hr exposure.
• Ideally fish should be diagnosed by an authorised or qualified technician.
• Carefully calculate dose rates according to manufacturers label.
• Remember that some chemicals may not be approved for use with fish that are for human consumption.