Help understanding ph

[Something Fishy Here]

So according to my local water report ph from the tap is 7.3. When i test water from the tap it looks like mid 7s. I'm terrible at distinguishing color shades on these tests though. When i test my tank water it comes out over 8. Does ph rise with aeration, oxygenation, and co2 offgassing? I have a couple chunks of mopani driftwood in the tank, stoney river aquarium sand which claims to be inert, and a few rocks, none of which are limestone or coral based. Any thoughts why there's these differences in ph?

 

[duanes]

In most cases, tap water is under quite a bit pressure in the distribution system, until it is released from the pipes when the tap is opened up.
While under pressure, there can be many gases trapped in it. Including CO2, which tends to keep pH down.
As water comes from the pipes, that trapped CO2 is released into the air, and can start to raise pH almost immediately.
You can do a simple experiment to check the gases trapped in your tap water.
If you draw a clear glass of water, (and if your tap water is super saturated with gases), it may look a bit cloudy with micro bubbles.
These bubble will rise, and the water clears from the bottom up (the pH may also rise at the same time).
This especially happens in winter, in cold climates, because the colder the water is, the more saturated with gases it can hold.

 

[Something Fishy Here]

Thanks, that makes a lot of sense.

 

[TwoHedWlf]

It's possible that the water in the mains will have a high CO2 level. I think the local utilities water tests should take that into account, letting the water outgas before testing? Anyway, easy way to confirm is to fill a bucket with water and then test it a few days later.

Probably as, or more likely, is that the contents of your tank are raising the PH. Crushed shells, coral/limestone in the gravel is super common.

 

[neutrino]

Not unusual. My water is 6.4-6.6 pH from the tap. I do nothing to it for my SA tanks and it settles like clockwork to 7.4 (my Cyphotilapia tank I buffer). I agree with the CO2 explanation.

 

[Something Fishy Here]

Yeah, i don't have anything in the tank that could raise it. It seemed weird that it was that low on the report anyway, our water comes from an aquifer trapped in limestone. Heavy mineralization etc but very stable, no seasonal shifts.