Originally Posted by stinkyattic

Use your commercial PLANT pH up/down- not the kind for pools- ad add it dropwise until the fertilizer solution is at the correct pH for your grow style.
The ideal 'middle' of each range is given here:
Hydro 5.9
Soilless 6.4
Soil 6.7
If you find your soil, for example, is giving a runoff that is too low, water with fert solution that is lightly HIGH- around 7.2- until you see that the runoff is in the correct range. If the runoff is too HIGH (much less common), use ferts at 6.2 until it improves. It's easiest to do this as a flush- all in one shot.
Be careful of shocking the plants with water that is more than a full pH point off their ideal range, even as a flush solution.