pH drastically lower in warm weather AC vs winter...how can this be?

[Randy Holmes-Farley]

Central head and A/C. Both electric.

The increased alk demand is always met by increasing the 3 part dose. In early September, it was 24ml/day of alk, now it is 26.4ml/day.

As mentioned, bigger temp differentials inside to out drive more air flow. If you do not open windows, there’s no reason to assume winter pH will be higher or lower than summer pH. A lot of factors go into determining indoor CO2 levels around the tank, which I assume is the driving force (and assuming accurate measurements).