You could do large scale water change with water treated with chloramine, depend on the type of fish or the type of dechlorine chemical used. As in this case, only the mahseer were stressed and killed by chloramine in that 10-15 minutes window. Other fish in same tank were not effect
I agree with you. I was referring to the people who never use conditioner, or "dechlorine chemical" as you put it. If the cost is an issue, buying a container of the powder form of Prime (Seachem Safe) would cost just a few pennies per water change. Why risk losing your fish over a few pennies? Again, I'm talking to the people who claim that treating tap water is a waste of time/money. This thread pretty much proves that chloramine can be lethal to some fish and at the very least most likely harmful to others.