lots of leaves dropping off. please help!

Mostly the leaves lower down on the plant or near the lower-middle are kind of withering, turning brownish maybe gray in patches, some are soft, some are dried out. when these leaves are bumped, they drop off of the branch they're growing from with zero effort. some fall by themselves, some seem like perfectly fine leaves and they are disconnecting from the rest of the plant with ease. big ones, brand new little ones, don't know if this is a bad thing or not. is it just because they are lower and mostly shaded from the 400w of CFL lights, they're not getting enough light to live? upper parts of the plants look great, just switched to flowering a few days after seeing the leaves do this. it's a hydro dwc, fox farms schedule 2nd week of flowering now.

any advice or what you think this might be, please let me know!
if you need any more information to make a diagnosis, just ask.

did you notice that the leaves did it alot more when you switched it over to flower? if you can look at the roots to see if they are white or are they brownish the latter usually means you have fusarium wilt. i have been fight a case of that for almost 6 months and let me tell you that it gets worse. the only thing i have used to any success is hydrogen peroxide dilluted to 7:1 ratio with water

If it occured after you started the flowering phase then this is "normal" for many growers. I dont like to see leaves falling off during flowering (esp early stage). Often times the nutes for flowering do not provide enough nitrogen so the plant start to use what it has in order to feed itself the rapid growth during early flower.This could be the case. I also use foxfarm and I can tell you that the scheldule doesnt provide no where near enough for early flowering. I have to add Cal-Mag which has a little nitrogen and up the scheldule a little bit.

Hope this helps and good Luck!