brown tips

Hey guys so im having some trouble while in preflower. Forbidden runtz auto day 45. She was lush nd healthy in veg no issues but noticing in pre flowering her leaves r getting a lil skinner and burning at the tips. Ive been feeding light nutes only for the past 4 days maybe 1/4. Currently using...

Im growing a critical purple auto flower I'm using 585 watts of led lights I got my watering schedule down I'm using.less.then the recommended amount of fox farms.big blooms blooms but I'm wondering why the bottom fan leaves on my plant have yellow brownish tips and there's one set.of.leaves...