Fluorite is lowering my pH

According to the bag it's not supposed to affect the pH at all, but I've just set up a new 90G and it appears to be the only cluprit.

I have water, slate, and some other stone in the new tank and nothing else. I have taken samples of each stone and let them soak overnight in buckets of water and they neither affect the pH nor Hardness of the water. However the fluorite appears to be bufering the water from my first test. I'm goign to let it sit a overnight to be sure, but there is nothing else that I can tell is doing this. There is nothing else in the tank!

The tap water after sitting overnight tests as a pH of 8 and a KH of 7-8. The water in the new tank however is a pH of 7.4 and a KH of 4-5. Has anyone seen Fluorite buffer the pH like this?

I still have to add the few pieces of Mopani wood, which I'm assuming will also lower the pH even more. The is becoming troublesome being that I have a pressurized CO2 setup that still needs to be set up.

Does anyone have any ideas? I'm quite confused about this.

Well I guess it's not the Fluorite, and was just the water needing to settle over night. There is still however something that is causing the pH to drop. I had been testing leftover rocks, but I guess that I will have pull the ones in the tank and test them. I wold have assumed that they were the same as they are the same kind of rock.

This is all VERY puzzling.