Stickstoff Mangel in der 4. Blütewoche ?

Absolutely nothing to go on other than visual id say it's uptake of iron. Typically not from a lack of iron in the soil itself, but because the iron is in a form the plant cannot absorb. While the lack of iron in the medium is a possibility, the disruption of its uptake almost always comes down to high pH and nutrient imbalances in the root zone.Low soil temps. And/Or oversaturated medium. High Ca and MG can antagonize iron. A possible long shot is when one is irrigating with "hard" water that has high levels of calcium bicarbonate, the bicarbonate ions can raise the pH of the growing medium over time and directly interfere with the plant's ability to absorb and utilize iron. Hope you get her back in shape, great grow so far! Nice nug formations. Best of luck.