Ich habe heute bemerkt das ein Blatt braune Flecken hat, ich weiss nicht was es sein könnte, die Lampe ist 40cm entfernt vom höchsten Punkt der Pflanze.
As you are growing full organic, don't panic. I looks to me as a kind of temporary fertilization inbalance. The nature will solve that, I would just wait another week.
It is showing magnesium deficiency. First check run off ph to make sure soil ph is in range. If it is then add cal mag or even epsom salt if in a bind.