Do you know the actual parameters of the well water (ph, gh, kh, tds)? It would have to be on the extreme side of hard to cause any problems with most fish. I'd definitely recommend switching to well water or half and half, but test the parameters first so you know what you're working with.
We've all had our moments where we said "I know I'm supposed to ____, but my fish are just fine." Just because they seem fine, doesn't mean they're as happy/healthy as they could be, and doesn't mean it won't cause problems down the line.