Nährstoffmangel?

Yeah, doesn't look good. Are there two plants in that pot? Half the plant is below the rim of the pot. The roots might be root bound .Even the seedlings in your diary post aren't healthy. That's from either poor lighting or toxic soil but her environment is crucial to. Is the temp and humidity right. Is there airflow?At this stage in her life I only have to water about every 7-10 days, 5 gallon pot. Yours look like 3-5 gallon, but medium also determines that. If they aren't very light when you lift them then they don't need water. If you know you have been watering correctly and not sure about how she's been feed, then I would transplant into fresh soil although that would add some stress but she's really hurting now. There's even deformation of new growth. If nothing else, back off everything like the other comment said. Make sure PH is good in soil and water. Wouldn't hurt to check TDS in runoff . Make sure lights are correct and temperature and humidity. Take your time and don't try to rush the process. Good luck. There's many good videos on YouTube from successful home growers and what they do.

Looks like your plant is showing signs of stress—possibly from overwatering or nitrogen toxicity. The dark green, clawed leaves are a classic sign of too much nitrogen, and overwatering could worsen it. I’d let the soil dry out a bit and ease up on the nutes, especially anything high in nitrogen. Also, ensure your lights aren’t too close and you have good airflow. It could be a combo of things, but dialing those in should help it bounce back.

Either too much light or a deficiency Try calmag

da die Blattspitzen auch braun bis schwarz sind, könnte es evtl. ein Nährstoffbrand (Überdüngung) sein oder der pH-Wert ist nicht ganz korrekt

Hi friend, I actually think that it is an excess of brightness that is ruining these excellent shoots....remember that too much is not always a good thing😎.