I have a recent similar circumstance. Our well water is PH 6.6 GH
but it is fed by mountain springs. I recently tested the water in the pond which holds the water before it trickles down hill through the ground into the well and the GH
were much lower 5 and 4.
But I do know there are a lot of rocks down the well that would account for that.
The strange thing to me was that a few months ago in the winter time, the PH was higher....so I think I must have been doing something wrong before. The water in my 55 gal
planted stays consistant at 8.0ph but I think the rocks are responsible for the increase.