Stop spreading psuedo-scientific alternative-medicine falsehoods. Dandruff is in no way caused by a "PH imbalance on the skin": http://www.mayoclinic.org/diseases-conditions/dandruff/diagn...
Sure, dandruff and 'dry skin flakes' are separate things entirely.
Dandruff is generally regarded to be caused by the fungus Malassezia. This fungus does not enjoy an acidic environment.
(Healthy) human skin tends towards pH 4-5 (there seems to be some debate). Malassezia likes 5-8 (again, some debate). Reducing the pH / increasing the acidity would appear to have some non-psuedo, non-alternative-medicine, non-falsehood foundation.
If the latter, I can probably agree. If the former, please do some more research.
https://www.urmc.rochester.edu/encyclopedia/content.aspx?con...
Maybe that's because vinegar isn't a staple in the hair care aisle at Walgreen's.