Virgin Grower, Nute Issues?

so i've got some plants, a few weeks old. just went under 250 watt MH and now i'm getting yellowing, i am guessing it's a deficiency from what i've read. just want to be sure on what the problem is and how i should go about fixing it.
PS. i've got them in soil, used miracle grow, pre fertilzed mix

Bro u´re using MG grow or MG nutes i didnt get that...anyway if ure using MG soil u better check the soil pH...it should read between 6.2 and 6.8 and pH ur water aswell...tell us the results

using MG soil, soil ph 6.8, water ph 6.8
another question while i'm at it...when i water how wet should i get the soil? enough to get runoff out the bottom of the pot or enough to make the the soil moist??
also, i just got fox farm grow big, made a nute solution that's about 600 pm, is this ok to use for my regular watering solution? right now i'm watering every 3 or 4 days just enough to make the soil moist and they are definately dry by the time i water again

any help would be great, i didn't know growing weed was such an in depth prosess, but a beautiful plant in the end will be worth it

I allways soak and dry the soil the roots develope much better and i dont have the trouble of watering every day...dude the ppm deppends on how old u´re plants are i´m feedin about the same (1.2 EC) to 3 week year old plants in a hydro bubbler and they love it...but i assume that if u´re not getting nute burn u should be ok...and yes growing Cannabis is a fascinanting universe its amazing the quantity of info one must get to feel confortable growing a few plants, but imo it´s well worth it, lot´s of fun and at the end u get a beautifful reward...Peace and Pot

THANK YOU
will post some updates later and probably be back with many more questions as my babies grow