Satorsanswered grow question a year ago Hi Tomatenmark69.
It’s could be over fertiliser. Flash with ph balanced clear water, check run off water ppm and ph. If ph high try to reduce it with clear water, if ph low then try to increase ph level. If ppm is higher 1500ppm, stop feeding with nutrients but using only ph balanced clear water for one week minimum and keep monitoring watering ph and ppm scores. When everything go back in normal ph 6-6.7ph, but ppm max 1000ppm start add nesesery nutrients depend how fare you are.