Oh, mine did that too on the leaves tips.....I put 1/4 tsp of baking soda with my nutrients when I watered and it kept other leaves from doing the same thing and was fine.
What nutrients are you using?
https://www.rollitup.org/marijuana-plant-problems/691705-marijuana-plant-problems-mini-guide.html
This thread is very useful!
also for your lighting schedule, you're going to want to keep a consistent schedule while in veg. They're regs right? And not autos? I think maybe an 18/6 for veg and 12/12 for flowering. Look it up a lil and see what light schedule you'd prefer, but don't keep switching it up during veg. ^^