Some general comments as there seems to be a misunderstanding about fish requirements.
Fish are living creatures. Each species of freshwater fish has evolved over thousands of years to function in a very specific environment. Environment here means the water parameters (because freshwater, unlike marine or ocean water, is very different depending upon where it occurs), habitat features (substrate, wood, rock), light, and water flow. The physiology of the fish requires these environmental factors, and when any of them are different from what the fish requires, the fish has a more difficult time functioning. The fish may still live, but with considerable effort. This causes stress, and stress is the root cause of 95% of fish disease. It also weakens the fish, and the metabolism is affected.
Surviving in less than ideal conditions is not at all the same as thriving in what nature intended. The aim of all of us as aquarists should be to provide the closest reproduction of the natural environment/habitat for the fish we keep in aquaria. If this is not our aim, we have no business being in this hobby, because not doing this is outright cruelty to the fish.
The extent to which a species can adapt to different conditions is very limited. One does not and cannot change the physiology of a species. The needs are built in to the physical structure of the fish, and programmed into the DNA for that species.
Fish are living creatures. Each species of freshwater fish has evolved over thousands of years to function in a very specific environment. Environment here means the water parameters (because freshwater, unlike marine or ocean water, is very different depending upon where it occurs), habitat features (substrate, wood, rock), light, and water flow. The physiology of the fish requires these environmental factors, and when any of them are different from what the fish requires, the fish has a more difficult time functioning. The fish may still live, but with considerable effort. This causes stress, and stress is the root cause of 95% of fish disease. It also weakens the fish, and the metabolism is affected.
Surviving in less than ideal conditions is not at all the same as thriving in what nature intended. The aim of all of us as aquarists should be to provide the closest reproduction of the natural environment/habitat for the fish we keep in aquaria. If this is not our aim, we have no business being in this hobby, because not doing this is outright cruelty to the fish.
The extent to which a species can adapt to different conditions is very limited. One does not and cannot change the physiology of a species. The needs are built in to the physical structure of the fish, and programmed into the DNA for that species.