Please help we cant figure out whats wrong?

ok so this is the beginning of our 4th week, and weve got alot of yellow on alot of the leaves. we dont know what to do please help!!!

magnesium or zinc deficiency

I would guess the same thing. Magnesium or zinc. I'd try magnesium sulfate first. Get yourself some Epsom salt and see if that helps...

Here's a link that talks about how much to use in the thread: https://www.rollitup.org/hydroponics-aeroponics/284588-epsom-salt-usage.html