Chloramines and fish don't mix
Water may be safe to drink, but it may not be safe to breathe. While people have no problems with tiny amounts of chloramines, fish do. When water is swallowed, it is immediately neutralized by the digestive system before it reaches the blood. However, when fish breathe the water, it enters the blood stream and chemically bind to iron in the red blood cells, making it difficult for the cells to oxygen. Sometimes, they even "suffocate" from lack of oxygen. Chlorine alone is also harmful. Thats why, before adding it to ponds and aquariums it must be conditioned.
One way of removing chloramines is by neutralizing them with chemicals sold originally at pet stores for removing chlorine. Granular activated carbon (GAC), a filter material for aquariums can also be used to remove the disinfectant. However, the carbon must be high quality and the water must be filtered long enough to make sure the disinfectants are eliminated.