Often (but not always!) there is a faucet outside for garden use. This is not run through the softener or any other filter.
Try taking a sample from there. Do it this way:
Run the hose bib for at least a minute before you start to take the sample. Run it longer if you know there is a long run of pipe from the pump to the house.
See if this water has the same GH as the other samples.
If it does, here is what I would do for soft water fish:
Use water that has not been treated. (no softener, no filter- right out of the well)
Add GH booster, a source of calcium and magnesium until the GH was in the right range for the fish. Many soft water fish are good with GH of 3 German degrees of hardness. This is a good minimum for most aquatic plants, too. Angels will be fine in this.
Be careful and read the label on the GH booster. Some contain salt (sodium chloride). You do not want this in the water.
Seachem Equilibrium is good, and so is Barr's GH booster. These also contain potassium. At the low level you are using them it is not much, but some.