Leaf

Lack of calcium. Not a potassium deficiency.

The leaf damage in the photos shows a Calcium (Ca) and early Magnesium (Mg) deficiency, not light stress or pest damage. Visual indicators: Brown, irregular spots between veins, mostly on mid-aged leaves → Calcium deficiency. Light green or yellowing between veins on younger leaves → beginning Magnesium deficiency. Spots spreading from the inner part of the leaf outward → typical when uptake is restricted at the root zone. No curling or burn at the tips → not caused by light intensity or heat. Likely Causes 1. Incorrect pH in the root zone Calcium and magnesium uptake drop sharply if the root-zone pH is below 6.0 or above 6.8. Even if the irrigation water looks fine, substrate pH can drift over time. 2. Nutrient imbalance or lockout High levels of potassium or phosphorus can compete with Ca and Mg uptake. Sometimes caused by overfeeding or by residual salts from earlier feedings. 3. Environmental stress Very high humidity or irregular watering (dry/wet cycles) can reduce transpiration, limiting nutrient transport. Recommendations 1. Check pH of both irrigation water and runoff. Aim for a root-zone pH between 6.2 and 6.5 in soil. If runoff is outside this range, a light flush with properly adjusted water can help rebalance the medium. 2. Ensure stable watering habits. Keep the substrate evenly moist; avoid long dry periods or heavy saturation cycles. Consistent root-zone oxygenation helps nutrient mobility. 3. Optimize environment. Day temp: around 24–26 °C, night: 20–22 °C Humidity: 45–55 % in flowering phase Air movement should be gentle and indirect; passive airflow and exhaust ventilation are often enough. 4. Observation period. Damaged leaves won’t recover, but new growth should appear green and healthy within about a week once conditions are stable. Bigup and be nice ganja farmers 💚🙃

PS : P def was my first impression, but it is more likely calcium deficiency caused by excess potassium https://i0.wp.com/growithjane.com/wp-content/uploads/2025/02/cannabis-calcium-deficiency-caused-by-excess-potassium-grow-with-jane-1-scaled.jpg?resize=768%2C1024&ssl=1

Looks like the early signs of a potassium deficiency the brown spots and yellowing between veins usually start like this. Double-check your pH range (6.0–6.3 in soil / 5.8–6.0 in coco) and make sure runoff isn’t building up salts. If pH is fine, slightly increase your bloom nutrients or add a bit of K supplement. New growth should come out clean and green soon

Insufficient calcium provided or something locking calcium out.

Ca def