Zu viel Dünger ?

Yes, very over fed. Remember too, when growing in soil, it is a schedule of plain water/plain water/fertilizer/plain water/plain water/fertilizer...........

Might be a pest infestation. It's hard to tell from the pictures. When you say too much fertilizer ON the leaves? Does that mean you are foliar feeding? If so I would back off for a bit. I would even back off of heavy nutrient dosage or any sort of high stress training until you figure this issue out. Adding extra stress factors could act as a 'multiplier' of sorts and really do damage right now. There's a few products I would recommend to help. I use diatomaceous earth when I'm in vegetation. Sprinkle some on the leaves and then put it directly on the soil when it's dry to kill any insects on them. Also, Dr. zymes is an organic pesticide that works wonders. Usually nutrient deficiencies show up in rust colored spots close to the veins of your leaves. Or yellowing leaves for a deficiency and burnt tips for nutrient (nitrogen) burn.