Chloramines and Fish
Because chlorine is extremely unstable and dissipates quickly from water, chloramines were developed and are now primarily used to maintain water quality in pipelines that are often quite old and extend for many miles. Chloramine (NH2Cl), an inorganic compound that is a combination of chlorine and ammonia, has been used for more than 90 years. But its proliferation began in the mid-1980s. Of the three types of chloramine used in drinking water, monochloramine, comprised of chlorine and ammonia, is most often applied to public water systems.
Chloramines received a terrible reputation when water utilities added the compound and failed to adequately educate the public because it resulted in massive tropical fish deaths for no apparent reason. The Internet as we know it today was not available then, so aquarium publications, fish clubs and pet shops did their best to spread the word for coping with this problem.
Chloramine is an invisible compound that fish take directly into their bloodstream through their gills. Fish exposed to this compound experience stress, damaged and burned gills, erratic behavior and sometimes even jump out of the aquarium. It is a horrible, yet preventable, death. Fish seen gasping at the water surface with rapid, labored breathing could be suffering the effects of chloramine poisoning (especially if these symptoms occur following a water change).