It is damaged caused by the leaves touching the wet earth when the lights are off and the leaves then droop downwards. It is not a real problem and often occurs to the lowest leaves on young seedlings. Continue with your current care routine and all will be ok. The lower leaves usually go yellow and drop off at 3-5 weeks of age and is absolutely a normal thing and nothing to be concerned over. Hope this helps,.... Organoman.
Need to check soil ph run off. Should have 20 to 30 percent run off. Need to be below 6.5 but above 5.8 is idea ranges depending on grow medium. With coco a 5.8 to 6.0 is great. Good luck and happy growing 🌲🌲🌲👊