Mangel oder Überschuss?

The yellow leaves and red stems could indicate phosphorus deficiency or a nutrient lockout. A lockout often blocks other nutrients like magnesium, calcium, potassium, and nitrogen as well. The yellow leaves might suggest a nitrogen deficiency, which can be normal during the flowering phase, but if it occurs too early, it indicates a deficiency. Magnesium and potassium could also be involved if the leaves become pale or spotted. Since you're already giving CalMag, a lockout could be blocking these nutrients. Your EC value is within the normal range, but keep an eye on the pH (6.2–6.5) and the runoff EC to avoid salt buildup (which is rather unlikely with BioBizz). If things get tight, just flush and then start fertilizing slowly again.