Wie oft Calmag Dünger anwenden?

This isn't a calmag problem at all... I would be thinking it's a phosphorus issue - but more importantly, a problem with your pH... the stems are all red, the pattern to the damaged leaves all say the pH is most likely not in a good range. If you're growing in soil, you need to maintain a pH between 6.0 and 6.5 (6.3 is the sweet spot).... if you're growing hydroponically, the pH should range between 5.5 and 6.2 .... And since I don't see ANY mention of pH in your diary, have to believe you're not paying any attention to it... Get it under control! The best purchase I ever made for the success of my grows was a pH pen... they are worth their weight in gold. Good luck...