A certain fish that comes from a certain water will like a certain hardness level, along with a certain pH.
However, most freaswater fish can addap to many levels of hardness and pH, as long as those are not extreme. If your water is TOO hard, you can try using a mix of tap water with distilled water to soften it a bit. You could also try a reverse osmosis unit, but those are expensive.
In the last case, you could try keeping "hard water" fish. You can do some research and find a fish that will enjoy your hardness level.
BTW, what are your water kH and gH readings?