Rootzone pH and Nutrient Uptake
Nutrients become available to plants at varying pH levels. Most plants prefer their rootzone to be slightly acidic, including cannabis.
Below you can see the range at which each nutrient is available for the plant to uptake. A pH of 7 is considered neutral. Anything higher is alkaline and anything lower is acidic.
If the pH of your medium becomes too acidic or too alkaline, the plant will be unable to uptake certain nutrients and will manifest in the leaves as a deficiency. This can be misleading. What looks like a deficiency could actually be a pH issue and adding more nutrients can make things even worse. This is why it is beneficial to to keep your rootzone within a certain pH range.
Below are two high resolution charts you can download for personal use. One is the optimal pH range for growing cannabis in soil and the other is the optimal pH range for growing in hydro/coco coir.