Leaf

That's a calcium deficiency for sure. They're looking a little low in nitrogen too buddy

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