I have an Oakton ph tester.I have calibrated it to a 4 and 7 buffer solution.The water that I have left out in a 5 gallon bucket for over 3 days is registering at 8.2 , while my tap water right out of the tap is 7.1 . Filtered water ( through a Britta filter ) is at 6.7 . Anybody know why there...