Does the water level of your sample matter for pH measurements? I was under the impression it didn't really matter that much, but it would be the only test in the kit that didn't need a perfectly sized sample.
But if my theory was correct, I wouldn't think a small variance in sample size would NOT cause you to get 8 one minute and 7 another.
One other shot: do you happen to have another test kit of some kind and have used the bottle for it in your Taylor K2006 kit comparator tube? I have a Taylor k-2005 or something or other, and once used the phenol red from that kit, and got a way higher pH reading. But I quickly realized my error.