I do have test strips. I have
The rocks in the water aren't sealed, they're just slate rocks I had some something else that I cleaned up. Then the banks of the pond are a mix of aquarium gravel and fluval stratum.
I ran it on my pond today and came back with a GH of 15 to 20, KH of around 10 and a Ph of 7 still. So the water is picking up little bits of something from somewhere to nudge the hardness a bit. I'm not sure if that little dribble of water is enough to be knocking CO2 out of the water for the KH though.