Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Well, my first comment is that GH is really the first concern. Make that right for the fish is the first step.
After that, the KH. Not because the fish seem to mind, but because it is a buffer for the pH. As a VERY general guide, most fish that come from soft (low GH) water, also prefer a lower pH. The range is usually quite wide in pH tolerance, as long as the GH is right. I generally try to keep the KH roughly the same as GH. That way the hard water fish also have high pH, and the soft water fish have low pH. It may vary some, but it will pretty much always be at least in the right range.
With well water that is so different, low GH, high KH, I would want to remove the KH. Blending well water with RO, and adding some minerals for the right GH would be one option. You could test this by buying a gallon of RO or distilled water and running some tests.
Try different blends of well water + RO until you get a KH under 100 ppm (4-5 German degrees of hardness). Perhaps 25-30% well water + 70-75% RO.
Then add some GH booster until the GH is around 3 degrees (50+ ppm).
If you want to keep black water species, then filter the water through peat moss to add the organic acids these fish need.
That sort of blend will probably be really good for pretty much all the soft water fish. You might need to fine tune it if you want to breed certain fish, or keep wild caught.
Totally the other way:
Use well water and add a lot more GH booster, then keep hard water fish. Many Rainbows, most Live Bearers, Rift Lake fish (not just the Cichlids).
Most aquarium plants will tolerate either end of the spectrum of hard to soft water. There are a few specialist plants that really do require certain water, but these are not very many.