Wie bekomme ich es hin, dass meine Pflanzen wieder vernünftig wachsen oder sieht alles legitim aus?

Looking at your diary few things there is no EC/PPM readout of your solution your feeding with. You should know the concentration. I'd also do this with you feed current NPK is 1.78-5.06-6.07 - nitrogen is to low in comparison with the other numbers. I would also look into adding in some extra calcium and magnesium via calmg, that will also boost your N by 1-0-0 It would work well with your current feeding guides as long as the EC is in check. This is a recommended feeding guides by the manufacture on your feeds. bn-x-cel 1-0-0 lower it to aorund 1ml/l vs 5ml/l its a dilution ratio of 1:1000 Vitasol is the same 1-0-3 keep it aorund 1ml/l its a dilution ratio of 1:1000 PK booster is 0-13-14 lower it to aorund .75ml/l Its dilution ratio is 1:1500 Alga bloom is 3-2-5 use about 4ml/l its dilution ratio is 1:250 new npk ratio is 1.25-2.93-4.62 - i would like to see P just a tad higher but it works. Good Luck!