Help, Please, plants are getting sick...

I have had things going for about 2 mos. in my dwc. The babies were doing super fantastic until may 10th they started to show signs of wilting and getting a sick look, two days later the leaves are starting to curl a little and are getting a dry feel along with yellow looking patches coming through the green. it seems to be working its way from the bottom larger leaves up. :(:(:(

general hydroponic 3 part system
plenty of light using compact flourescents
18\6 for light timer
no pests visible
water temp is 72ish
room temp is around 70
humidity between 35-45%
PH dropped about 5 days ago to about 5
raised it a little with gh ph up to about 6, this was on thursday last week

any help would be great thanks all.

post pics but sounds like low nitrogen

Say Bro, Something that might Help. OK I have been using GHP-3part for ever, I have added Cal-Mag Plus, Pure Blend Original (Grow & Bloom), Liguid Karma, Silica Blast, Hydrogaurd, Hydroplex, all from Botanicare. They have really help the general health of my Plant's, & have taken care of any Def..

Thanks folks, here are some pics, as we can tell I am not a photography expert, hope they come through....:wtf: