Problem?

[Robbie762]

Hello everyone!
I'm hoping for some help this morning......
Background-
My first auto flower grow
4X4 grow tent, 400W HPS light, 4" inline fan and duct connected to light for cooling, multiple 6" fans and 1 16" oscillating fan
OF, perlite, HF.......perlite was added to the OF, soil is layered- OF/Perlite for bottom 2/3 of 3 gallon plastic pot,
layer of 1 tsp Great White mycorrhizae, 1/3 HF top layer.
White Widow auto Nirvana seeds........She's 18 days old today. She had some LST over this last weekend
Keeping my light about 18 inches above plant
No nutes as of yet. Just ph 6.5 tap water that I leave out over night to get rid of chlorine.
Problem: See photo- light yellowish spots on edges and middle of 1 fan leaf. Seems to be on only the one leaf.
Tent photo included also.
My first thought is some water left standing on that leaf while under the light. BTW, I'm doing a 20/4 light cycle
My temps are running 75 degrees F - 85 degrees F, Rh is all over the place from a low of 18% - 45%, but averaging about 35%
Thanks for any advice you could give......

 

[Proph]

You're on the right track.. Looks like either bleaching from the light, or a nutrient spill on the leaves.. That light looks super close in the pics.

 

[Robbie762]

You're on the right track.. Looks like either bleaching from the light, or a nutrient spill on the leaves.. That light looks super close in the pics.

Thank you..........I'm going to pull the light up another couple inches