WW 2nd Grow Problems?

[LDRunner]

Experiencing some potential problems not seen in my first grow. Have researched extensively and cannot tell if I am overwatering, underwatering or if I have a N deficiency. Any help would be extremely appreciated.

3 WW Clones, approximately 5 weeks into veg
I usually water every 3-4 days when containers are "light"
pH is at 6.4
Vegging 24/0 250W MH about 8" from plants
Temp steady 75F, Humidity 47%

WW1 pic is least effected, has added about 3-4 inches since last week.
WW2 second plant, also growing well, but the lower leaves are yellowing
WW3 third plant always been the runt, still growing, however, much slower. Entire plant beginning to yellow.
WW2 2-5 Plant #2 close up of leaves and other side of entire plant.

In my last grow I used CFL's, going the MH and HPS this time. Added additional 8"fan to cool ballast. Is it possible with the extra heat and ventilation that they are just getting too dry? In addition, I have not watered with any nutes yet. Could that also be the problem.

What type of time might be needed in order to correct? Was hoping to switch to 12/12 flowering after 6 weeks or so when plants reach 15 - 18 inches.

As always, thanks for any and all help.

 

[greenthumb1]

your plants look very hungry. Feed them at 1/3 strength and that should correct your nitrogen deficiency. Also, it looks as if they are over-watered as well.