Tap Water Ph

Can you please help me determine what the true pH is of my tap water? When I tested yesterday straight out of the tap it’s 7.2. Then I tested the same water today (have been sitting out for 24 hrs) and it’s 8.4!

How could the pH go up so high within 24 hrs by just sitting there?

Thanks!

 

What test kit are you using? I wouldn't be surprised if the pH goes up that much. I've seen other members with tap like that. Do you know the GH and KH?

 

Dissolved CO2 in the water straight from the tap lowers the PH (carbonic acid in it believe?) So when the tap water sits it releases the CO2 into the air and then the PH goes up.

 

What test kit are you using? I wouldn't be surprised if the pH goes up that much. I've seen other members with tap like that. Do you know the GH and KH?

API Freshwater Master Test Kit. I don’t know the GH and KH.

Dissolved CO2 in the water straight from the tap lowers the PH (carbonic acid in it believe?) So when the tap water sits it releases the CO2 into the air and then the PH goes up.

Oh ok. So technically my true pH would be the 8.4?

 

Yes, the true pH is what it is at now.