Make sure you use Ph up/down that is made for growing. May seem like a stupid comment but I have witnessed a few people that try to use stuff made for fish tanks and although it will work fine to ph water, it doesn't have the buffers needed to properly ph water and nutrients. Using those will cause your ph to go crazy. In the beginning I used whatever ph products the maker of my line of nutes made but over time I realized it didn't matter as long as it was meant for growing. Of course now I don't use salt based nutes or ph products...