Over-watering cannabis. Is it that bad? How about over-feeding cannabis?
BROWNDIRTWARRIOR says to mimic nature. Plants aren't usually bombarded with nutrients or in standing water.
Over-watering and over-feeding cannabis plants can lead to powdery mildew, fungus gnats, root rot, and burning.
PPM is one tool used to help measure nutrients. BROWNDIRTWARRIOR gives several other tips in his video below.