When I started out........most of mine looked exactly like those.... EVERY case is different but for me what worked was...good ole Cal-Mag. A teaspoon per gallon of water and you are good to go....
Your soil looks really dry....Also, if you use organic fertilizers, you dont need to worry about burning em up.. I have double and even tripled the recommended dosages without any problems.
What strength are you feeding at.....Full strength, half?......Yellowing that young is nute deficiency or over/under watering.... But, like I said, EVERY case is different...
When I stopped worrying about drowning em or burning em up.....I havent had a problem since..... My biggest worry now is making my own strains.. Good Luck...Happy Growin