High ClassicKellerWiese,
The leaves fall off due a wrong watering schedule. You need to let the top layer of the soil about 2 inches (5 centimers) dry out completely before watering again.
The deficiency comes from a wrong pH so the plant can not uptake the nutrients. You need to water with a nutrient solution with a pH from pH 6.2 and water till 20% runoff and do NOT water again till the top layer is completely dry to prevent lack of oxygen at the roots.
Happy Growing Buddy! 💚