(Sorry I couldn't resist being a smart alec)
Lowering water hardness is a lot of work and/or expensive.
I had/have this problem too and did a little research. Other than moving, here are a few options:
1. Water softener. Bad in my opinion. They are expensive and only remove one type of hardness from your water.
2. Buying distilled water. Fish need some minerals in their water so give them part distilled and part tap. In the long run, this gets expensive. I found distilled water for $.69 a gallon, and over time it adds up to quite a bit.
3.
RO+
DI (reverse osmosis + deionization) These filters give you basically distilled water. This is the route I chose. I bought the cheapest one I could find on ebay- $100 with shipping. It took some work getting it set up and stopping the leaks, but wasn't too bad. If I knew what I was doing it would have been a lot easier. I like not having to go to the store for water.
4. Get water from relatives somewhere else. This can also be a lot of work.
If you're happy with the health of your fish, then I wouldn't worry about it.