Sometimes just adding water if the ph is low after you have added the nutrients will lower the ph.If i did not have the real ph down then i would use lemon juice straight from a fresh lemon this way there is no additives.
Baking soda will raise PH and also stabilize it a bit longer also .. Also Cider vinigar will Lower Your Ph .. Some say it does not last But I have used it and its just the same as using PH Or down In a bind It works and is stable kiss-asskiss-asskiss-asskiss-ass