Originally Posted by psehorne
I let a small sample of beer sit overnight to go flat. The next morning it had dropped from 6.0 to 5.5 pH.
I checked the calibration of my pH meter when I first got it a few weeks ago. It read the 4.0 buffer as 4.0.; the 7.0 as 7.0; and the 10.0 buffer as 10.1. Close enough.
Maybe you breathed on it a lot.
The guy at my fish store says the pH of his tank drops when he has a lot of people in his house, or after a party. He says the CO2 from respiration of his guests affects the pH of the tank. Hence, he now has the fans over his tank pulling air from outdoors.
It's all very odd since we keep the alkalinity of our tanks relatively high to prevent pH swings.