well, judging from your post and use of "city" water I am guessing you were previously doing water changes with well water?
In which case the problem would likely be chlorine or more likely chloramines which need to be neutralized when doing water changes. These are added to kill bacteria in city water supplies.
Chlorine (not as common anymore) is relatively volatile and will dissipate on its own within 24 hours if water is left to sit out or can be neutralized with many available products. It is very irritating to fish and literally burns the gills of the fish causing damage to this vital organ that can kill them quickly, or slowly cause cumulative damage over time with them then weakening and passing away days or weeks later.
Chloramines are a group of chemicals that are significantly more stable and will hang around in water for weeks unless neutralized (hence why municipalities like them more) . They cause methhemoglobinemia. This renders the fish's hemoglobin unable to carry oxygen from the gills to the rest of the body. This can also kill a fish rather quickly or cause them to weaken and dwindle until dying at a later time.
If this is not the issue give us some more info and someone will be able to help you.
Oh also you can usually look up a municipal water quality report with various test of the tap water listed to see if the water is not suited to the species, or test them yourself/take it to a LFS for testing.
In which case the problem would likely be chlorine or more likely chloramines which need to be neutralized when doing water changes. These are added to kill bacteria in city water supplies.
Chlorine (not as common anymore) is relatively volatile and will dissipate on its own within 24 hours if water is left to sit out or can be neutralized with many available products. It is very irritating to fish and literally burns the gills of the fish causing damage to this vital organ that can kill them quickly, or slowly cause cumulative damage over time with them then weakening and passing away days or weeks later.
Chloramines are a group of chemicals that are significantly more stable and will hang around in water for weeks unless neutralized (hence why municipalities like them more) . They cause methhemoglobinemia. This renders the fish's hemoglobin unable to carry oxygen from the gills to the rest of the body. This can also kill a fish rather quickly or cause them to weaken and dwindle until dying at a later time.
If this is not the issue give us some more info and someone will be able to help you.
Oh also you can usually look up a municipal water quality report with various test of the tap water listed to see if the water is not suited to the species, or test them yourself/take it to a LFS for testing.
