It is important to note that the PH scale is backwards to a common way of thinking; a number of zero, or one on the PH scale is referring to something that is very Acid, whereas a number like 13 or 14 is Alkaline such as hand soap or bleach. Right in the middle, also known as PH Neutral (7) are things like pure water, milk and eggs. Most coffee is around 6, just a little more acid than milk or pure water, so low acid coffees will raise the number slightly to become neutral at 7. Apple Juice is a number 3 and tomato juice is a number 4.
One last way to lower the acid level (or the PH Balance) of your coffee lies in the brewing process, and its also the most fun! It's interesting to know that cold brewed coffee will naturally reduce the acid of your coffee and you don't need to invest in any more hardware to start cold brewing at home, if not to lower the PH, but to enjoy a new process! Simply drop 80 grams of coarsely ground coffee beans into a pitcher and fill it with water, cover it and pop it in the fridge overnight. The resulting beverage will be delicious on a warm day, and its low in acid too.