Spot on leafs

Hello, growing my cannabis and veging for 3 weeks now and it appear that my plant seem to be sick.
with a dying leafs with a spot on leafs i would unplug the bdying leafs and i have no clue why it died.
Please help or explian. Thanks.

There is my growing and setup:

Strain: Headband, Blue island skunk, blue dream, OG lime
Growing in: Greentrees 24 buckets sys with 6 inch rockwool
Air Sysytem: All 24 buckets have bubble sys.
Solution: General Hydroponics (GH) feed twrice a day
Lighting: 4 T5, 4 bulbs light (Use on Veg only).
Room: 5 X 10 or maybe 4 X 9.
Temparature: 70 - 80 degrees
Water Temp: 72 degrees
Air circulation: Outtake air 725 CFM every 15 mins.
Air circulation: Intake air 150 CFM always on.
Air condition set to 72 degrees.

Misc adding:
Cal meg

Looks like bugs, 2nd pic looks like mag def.

or a calcium deficiency. If there's no bugs that's prob what it is.

sativas generally are picky eaters...i would suggest lighten nutes, and maybe foliar spray with epsom salts in case it is mag deficiency. good luck