The problem with our houses in the winter is they are closed up to keep the cold out. Without a continuous supply of fresh air our breathing and any combustion source in the house (furnace, gas stove, etc...) will eat up the O2. This lowers the Ph in our tanks. The CO2 scrubber is not the end all fix all but it does help. We were having the same 7.7 Ph problems and since installing it we haven't dipped below 7.9. Most of the time it is over 8.0.