Is this Leaf-Septoria? Had the small spots since a few days (looks like they don´t get really bigger) but some leafs start to die like picture 2. looks to me a bit like calcium-deficit, or i´m i wrong?
Would also guess cal mag. Number one deficiency under LED and never part of Feeding schedules while most people use them these days. First sign plant shows is purple stripes on the branches. Fastest way to act is with a foliar spray including a cal mag agent of your choice EC 0.4-0.6 PH 6.0-6.2 and also use it for next irrigations. Do you water with tap water or RO?