4 weeks old couple minor problems [pics]

10 by 8 room 15 plants , 2 fans, a 8 inch outtake 4 inch intake, room temp averag 75-80.. never used to have a humidity as i think my outtake was leavin it 0% cus my humidity thing didnt work now ive turnd the outtake off its 55% atm.

ive bin feedin water every 2-3 days the last 3 feeds ive put 10 ml of cana coco a & b twice and the last feed 20ml of each in 10 litres of water, as it says to give 40ml per 10 litres, im slowly introducin the feed as i have bat mix ( all mix ) soil and its ment to have enuff nutes in for 6 weeks.
heres a pic the first pic is my best plant that as nuffin wrong with it. the others are of one of my worst plants.

Bumpupupupup

3rd sticky from top def & tox , read it . fine info there good luck

have you tested your runnoff Ph?
do you adjust your Ph before you feed nutes?

targeting your nutrients+water to a Ph of6.3-6.8 should do the trick!
(depending on the Ph of your soil...which could be off by now....worth checking)

whatever deficiency or toxicity you have can probably be solved by adjusting your Ph correctly....