What is this? Deficiency?

Strain ak destroyer auto sensible seeds
In week 5 soil worm casting 70% 30 perlite and humus like potting mix.
Light 18/6
Nutrition npk 8 3 6 half of recommended dose every third day.
Why is bottom leaf started to show light green color and on some places like grey dots or grey edges.

Hey bro I see a little nute burn on 1 or 2 of the tip, although you shouldn't really see nute burn at half strenght, what nute line are you using??