I agree that strips are inaccurate, somebody did a comparison test on here and it really made the strips look bad.
Moving on, what test kit are you using? My test kit has both a high and low range pH test, and if I use the wrong test obviously I'll get the wrong result.
I am assuming this is testing tap water. Did you do the test the same exact way each time, or re-test to confirm? How far away is Room 2 from Room 1/Kitchen? I assume not too far because you say it's an apartment...
IMO, if you are testing correctly with a liquid test kit, something is up with your plumbing... either you have some sort of buildup in your pipes (IMO it's more likely the buildup is raising pH than lowering it - do you know if any plumbing work was done recently to one part of the apt and not the other?), or one faucet head is aerating the water much, much less than the others... there are a lot of factors involved when dealing with water from the tap.
On the other hand, if you are talking about 3 different tanks, then I'd look at rocks/sand and driftwood in the tank as possible pH changers, or your aquarium maintenance schedule (lax maintenance can cause pH to "crash").
