Yep... test in the same time frame... am and pm. That should give you a range of your highs and lows.I prefer not to drop below 7.9, but as you have researched, you can see that there's some pretty simple ways to increase ph by simply reducing co2 in your system(maybe a bit more aggitation at the water surface). Could also be that with the weather getting a bit cooler that your in-house atmospheric co2 is a tad higher which would effect your ph.