Any advise on this problem? (pics)

I think this might be stem rot but im not sure... and if it is then how do i prevent it from happening? Aslo the bottom leaves of the plant at the first node are wilting and dying is this a normal occurance as the plant grows? Sorry the pics are crappy. Thanks for anyones help on this.

What kind of lights?
How old are they?
How often do you water?
Nutes?

using two 3ft floros...mabye 2 1/2 months old...water with light spray every other day and roots when the top soil looks like its drying (probably every 5 days or so) during flowering i was useing expert gardener .02-.02-.02 in the spray and every other root watering. now im useing (starting very diluted) MG bloom booster 15-30-15 (same watering pattern). The plants have had the problem since a month into veg stage...