Too high of a pH and its too alkaline (oven cleaner) and too low it is too acidic (battery acid). I wouldn't vape either.
I would expect that a reasonable pH would be between 6 and 8, too far either way and you will notice it (harsh vape, extreme throat hit, unusually sour or metallic taste).
That said I have never tested my
juice, nor have I seen any advertised as "pH balanced".