Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
To keep soft water fish in this water, I would use a mix of RO and tap water. Set up some tests and see what ratio gives you the test results you want. With tap water that hard you will probably end up with 75% or more RO, and 25% or less tap water. Then I would use peat moss to further condition this water for soft water fish.
With such hard tap water you will not need to dose Equilibrium. You are trying to lower the GH, not raise it. However, Equilibrium also has potassium, so you would probably need K2SO4 to add potassium without raising the GH.
Do not skip with the fertilizers until the tank is well established. Then the substrate (if you are using a good one) will have sequestered some of the fertilizers and minerals the plants need, so if you skip some (vacation...) it is not such a problem.
I would also be concerned about trace minerals, and would dose with CSM+B or similar product. Maybe these minerals will come in from the tap water (often hard water has many other minerals in it besides the Ca, Mg and carbonates that make it hard water), but remember you are adding back just a small amount of tap water.