One thing that may have happened, was on your trip to get the water tested, CO2 mixed with the water while in the bag/Tupperware. ph has a tendency to drop while it is mixed with air...
pH swings are not a problem as long as it's only pH which changes; I've had planted tanks swing between 6.5 and 7.5 twice a day. pH is generally a red herring. GH and KH are many times more important. Fish are pretty much insensitive to pH.
Drop the PH up bottle and step away from the tank.... LOL your doin more harm than help...... if you really feel the need to raise your ph get a small bag of crushed coral and toss a handful in the tank
pH swings are not a problem as long as it's only pH which changes; I've had planted tanks swing between 6.5 and 7.5 twice a day. pH is generally a red herring. GH and KH are many times more important. Fish are pretty much insensitive to pH.
Drop the PH up bottle and step away from the tank.... LOL your doin more harm than help...... if you really feel the need to raise your ph get a small bag of crushed coral and toss a handful in the tank