Whats wrong with my babies!!?!?

I started growing these plants almost a month ago and until about last week they were looking pretty healthy. The first one was growing nice and tall, but suddenly the bottom leaves started turning yellow and rotting off. It seems to be working its way up the plant. The other plant has the same problem, with some light green leaves. It doesnt seem to grow any more, its stunted. Im not sure whats wrong with these plants becuase there was miracle grow in the soil so it shouldnt be nutes. Any suggestions?

P h ur water p h ur soil - ph ur drop off
too much light? I'm going thru same probs

I got a 400 watt metal halide bulb about a foot or a foot and a half away from the plant. Its on a 16/8 schedule so i dont think its too much light. but i did get rid of the aluminum. Both pots read with a PH of about 7.5-7.9. With the drooping, bushier plant i read that i meant be a magnesium defiency so i have been giving it some water soluable magnesium in a spray bottle on the leaves. Still cant figure out whats wrong with the plants.

How can i lower it? I heard lime or dolomite lime but where could i get that. idk!