Ph in fish tanks higher than tap ph

[catfishacr]

Hey, I moved and im trying to figure out the new cities water parameters. My tap ph is 7.8, and that's what the city reports as well. My fish tanks though show a ph of 8.4, no fish in them yet, they are just hooked up and have water in them, not cycling them yet either. I tested this by letting a cup of water from the tap sit for a day. It raised to 8.2.

Is this odd? I've heard of it lowering but both raising.

Tap water parameters: 7.8ph, kh is 214ppm, gh over 200ppm, also tap has chloramine I measure about .25 of ammonia.

Thanks!

 

[Fish Eat Fish]

Do you have rocks?

 

[duanes]

As hydrogen ions disassociate from water (while it sits in a glass) pH normally rises, and if there is any calcium at all in the water, it will neutralize acids (raising the reading).
To get an accurate pH reading in the lab, we would never let water sit for any extended length of time. And we always used magnetic stirrers to keep it moving.
So to get an accurate reading from your tank, the sample must be tested immediately after it is taken whether using litmus paper type strips, or a probe.

 

[fishguy306]

Another thing that can cause it is CO2 in the water. CO2 will drop the pH, as the CO2 levels in the water drop the pH will rise. I had water like that in one location I lived.