I read somewhere that you can soften water by boiling it, and decided to
do this as an experiment with my well water here in Crisfield, MD (about
1/2 mile from the Chesapeake Bay).

Before boiling, my water was 10 degrees (not ppm) general hardness, with
a pH of 7.8. After boiling for about 2 hours and cooling, it was 4.5
degrees general hardness and (this is the part that mystifies me) over
8.8 pH.

I don't have a test kit to measure carbonate hardness.

Any ideas what's going on here? If I add this water to my aquarium,
which is about 50/50 unboiled well water/distilled water with a net 5
degrees general hardness and pH pretty stable at about 7.8, is it going
to raise the pH of the aquarium by as much as I would intuitively think
it would?