The problem is that we simplify and confuse the whole pH thing when we really should be talking about essential electrolytes, which are both acid and alkaline. :) Apple cider vinegar is "acidic" because of potasium chloride, which is corrosive, and potasium is an essential electrolyte, one of the most essential.
It also has: Phosphorous, Cholerine, Sodium, Magnesium, Calcium, Sulphur, Iron, Fluorine, Silicon, plus many trace elements.
Overall, the effect is alkaline, jsut about the same pH as the blood, so it cannot upset blood pH, it can only help. :)