White Widow

My suggestions are simple : 1.What is your EC ? 0 is not the good values , at that stage you can reach 1.2 ec without any issues 2. Raise the humidity level around 70% , 50% is not good for seedling. 3. You can grow with a 24/0 light cycle but prefer a 18/6 with autoflowering strain or during photoperiodic veg stage to be sure that you plant can "rest " a bit

More than likely caused by ph imbalance. Check ur ph and get it balanced. I also notice what could be spider mite damage and potentially live mites. Also in pic 3 the white powdery patch in the top left corner is alarming what are ur humidity and temp levels like dont want an onset of fungal infection. I'd definitely be hitting that leaf with a micro scope to make sure ur clear of pests.