Plant continues to yellow

I am not over watering as they just went 1 week without water while I was away, it is not a magnesium deficiency as I watered them with epsom salts last time, and it is not nitrogen as I added a bit of high nitrogen nutes to some water when I fed him last time. He keeps on yellowing! The only thing I can come up with is that it is the PH of the soil, but everyone else is fine in that soil. I am going to buy a PH/moisture probe tomorrow to check it, but what else do you think it could be?

The plant to to the back left of the big plant is also showing the same signs but not as bad.

what are the temps and humidity and what are you using for lighting?
your soil doesnt appear to have any perlite and may have very poor drainage especially if you can go a week without watering and if you are using cups make sure you punch alot of holes along the bottom for drainage but you might want to transplant into different soil.
might get some superthrive or other vitamin that may help the plants develop a good root system.

why are you fertilizing those seedlings?
no ferts! they are too young! they are burnt to a crisp from overfert!
Adn yeah that soil looks shit too. what is it? is there a lot of peat in it? next time, better soil, and add perlite.

And finally, is it just my imagination or does the plant in the far left pic already have male sex parts on it? wtf!

Those are nanners for shizzle. Wow. Listen to Stinky.

Thanks for the help. I had to go out of town for a week and they needed to be transplanted into bigger containers so I just mixed what I had to get em started. I will go buy some promix today at the hydro store. Thanks for your help guys and gals!

Someone said it was root rot on another forum, is this likely?

These are also my lowryders who like to show sex after 20 days of popping out of the soil. The big one has huge balls developing. I wish it was a nice bud :( but I do need a male to get seeds for my next grow.