Sounds like using Sodium Thiosulphate to neutralize chlorine in water which contains the compound chloramine (chlorine plus ammonia) is potentially hazardous to fish because of the ammonia which would be released into the water during water changes, especially large 50% or more water changes.
Unless, is there a DIY way to then convert ammonia into ammonium, rendering it harmless to fish? If so, I'd consider using Sodium Thiosulphate in conjunction with this, but until then I'll stick with commercial water conditioners which remove both chlorine and chloramine.