HELPP my plants are dying!

i dont have a camera but im trying to get one. but here are the conditions.
about 85 degrees
home made dwc system.
abiut 1/2 strength general hydroponics Maxi Grow.
1 400 watt MH light.
a fan blowing on plants at all times.
ph is about 5.8
there is a mix of bag seed and WW and 1 AK47. all are about 4 inches tall.
i have one WW in soil beside them that is growing alot faster than htey are and the ones in DWC are dying. it looked like a MG or N def. but i thought i corrected it the bottom leaves started yeowing then the veins turned real dark green in some and other are just turing yellow and light green?
ANY IDEAS????????

alf

Pics is what help us out the most.

the yellowing is starting on the bottem with the older fan leafs...its a N def i think...how big are the plants an how old are they...peace

It sounds like Ph. your ph needs to be at 7 really. for soil. right at neutral.. Ph will kill your plants if your not careful.

started plants about 3 weeks ago and everything was going great. with in the last week one of my plants on its first set of leaves developed these yolow/brownish things that look like distorted rectangles spreading from the vein outward. i can now see it in the biggest leaf or the first set of 3 to come out now too!! and to add to that the stem has turned a purple almost eggplant color almost all the way up to the leaves any ideas?? what can i do to save her?

hopefully i can upload the pics but theyre not the best quality from a cell phone.