It is hard to tell IMO
. There are so many reasons why pH fluctuates especially when comparing two different tanks. Although both get their water from the same source, it is most likely a combination of reasons why the drastic change between tanks.
One tank may be stocked heavier, different temperature, different use of chemicals, filter media, different amounts of aeration, photosynthesis from any plants, and so many more reasons. Maybe change some of the setup, or some minerals.
Some people belive that pH is not that important. IMO
, it usually is not that critical, however sending the fish into shock is. I wouldn't stress about it to much but try get the two tanks as close as possible before moving fish.
From what I know, you shouldn't raise pH more than .2 per day whether natural, or chemical methods.
Please keep in mind this is all IMO
so hopefully someone else will chime in, lot of knowledge on here!