Potassium deficiency in cannabis
What it looks like
Older leaf edges scorch and curl while the center stays greener. Stems can feel weak. It shows after heavy fruit set when the plant is pulling potassium into the flowers.
What usually causes it
Ease back on nitrogen if the plant is dark and clawing, then use a normal bloom feed at the label rate. Scorched edges from too much feed look similar. If the tips were already burnt, do not raise the dose.
Check this first
Edge burn on older leaves, leaves looking scorched from the outside in. Confirm it is not light burn. Light burn sits on the leaves closest to the lamp. If the burnt leaves are shaded and low, check pH and whether the feed is heavy on nitrogen and light on potassium.
This is identification for a home grow. It is not a pesticide label and not medical advice. Follow your local law.