Ok so its my first time growing in coco. I have some Dinafem OG Kush, they are 3 weeks old since they sprouted. I started them on plain tap water, and in the last week I fed them twice, with an EC of 0.5, pH has been 5.8 from the start. I've no temperature issues, max 25c min 15c, and humidity is always in between 40 = 60%. They're currently under a 275 metal halide. It's the only plant out of the 5 showing these marks. It could be nothing to worry about but I want to make sure. Any ideas??