PH-Wert: 6,2
EC-Wert: 1,5
Temperatur: 20ºC
Luftfeuchtigkeit 68%
Schädlingsbekämpfung: Nematoden und Raubmilben
PPFD: 490 µmol/m²/s
at this figures (temperature, humidity, light) your plants won't take high EC...... have you ever measured, what's in the drain?
could be a lockout - though my initial idea is rather damaged roots due to bugs.
Since you already feed mites and nematodes, my first attempt would be to restore the roots/rootzone (low EC, mykos, bacteria, kelp)
Do you have any chance to lower the humidity..... or at least raise temperature a little, to avoid upcoming problems ( fungal infestation, mildew, budrott)?
Good luck 🙏