Water is the fishes atmosphere and serious consideration must be given to its supply and condition. The fish we keep in our aquarium can come from several different types of water depending on its origin. It is not too difficult to maintain a successful aquarium with a collection of fish from different continents. However some fish are fussier in their requirements and may die if given the wrong water conditions. If you plan to breed your fish then a much deeper knowledge of chemistry is needed. There are still many fish that have not been bred in captivity; this is due to us humans not being able to mimic the water conditions of their natural environment.
Chlorine and Chloramine are added to water to eliminate harmful bacteria in drinking water for human consumption, but are very toxic to fish, beneficial bacteria and plants. When first setting up an aquarium and whenever partial water changes are conducted, always use water conditioner to make the tap water safe for fish.
It is important to ensure that you maintain the correct water conditions for you fish. This can be monitored weekly by use readily available water testing kits. Most water chemistry can be altered by the vast array of products available today.