Was fehlt den Pflanzen?

Those spider mite will be sucking the juice out of your plant like little vampires, get some preditors in there to eat those first or they will take her down.. see how you go from there but it's not the end of her yet.... those mites are a massive pain if you have more plants stay away from them as the mites stick to your clothes and spread like wild fire... Good luck...

Check your EC and pH from the drain, it looks overfed to me and maybe even a bit too much water. Flush and let the soil dry out a bit to use up the nutrients, or you might be watering too little with too much fertilizer. The salt content in the soil would then be too high and oxygen uptake would be hindered... Work clean and try to combat the pests.

Incorrect feeding and spider mite infestation.

Plant look hungry for everything. Nitrogen and calcium. There is probably a ph issue thats blocking proper absorption. You also have a spider mite issue which is those little white dots on the leaves. That will also hinder growth and make them yellow and have issues. spider mites suck sap out of the leaves so theyre sucking the life out of the plant basically and it makes it hard for it to grow with vigor. Lost coast plant therapy or anything with essential oils in it works well. also safer brand insecticidal soap works well. i alternate between these two. both organic inputs and safe for edible crops.

Hey there it looks like a lack of nutrients brought on by lock out the soil ph is to low it needs a flush of a few gallons of plain tap water then a few cups of water with nutrients Also it looks like you have some powdery mildew going. Make sure you don’t have a humidifier going make sure to have an exhaust fan and a fan that moves the air around the tent if need a few fans Good luck

That looks like a clear nitrogen deficiency, especially given the uniform yellowing from the bottom up and pale, limp leaves. Could also be a pH-related lockout if feeding has been consistent – check your runoff pH to confirm. If you're running organic or reused soil, recharging with a balanced grow feed or compost tea might help both plants bounce back.