Kräuselnde blätter, verbrannte Sonnensegel spitzen, absterbende Blätter im unteren Bereich

Hey, it's unfortunately a bit hard to get all the info from a photo. Basically, it can be a combination of many things: temperature, humidity, light intensity, over- and underwatering, pH level, and nutrient content. I strongly suspect that you've been watering too often, which prevents the plant from breathing properly. Also, your pH level might not be right, which can lead to a blockage in the substrate due to salts. Check your watering habits and your pH level; sometimes less fertilizer is a bit better.