Urgent expertise needed

hi guys. i really need your advices for this one.
have transferred my 6 little babies, from 18/24 to my 12/12 room. for 2 weeks, everything was fine until last 4-5 days. two of my babies seems not well at all and i don't really know what is happening to them.
MORE INFO =
transferred from 18 to 12 25 days ago.
plants are under 400watts HPS, well ventillated.
ebb flood control 2 times a day.
after 20 days, two of the plants are having their leaves downwards and started to dry.
have already flushed all plants with water only since two days ago.
only two of the plants are showing these negative signs so far, the remain 4 are quite ok.

COULD ANYONE HELP ME BY SORTING OUT WHAT THE PROBLEM COULD BE OR WHAT'S WRONG HERE.

THANKS

Root bound or maybe nuet lock?!|?! What are you feeding them? How high is your light? They look pretty lanky!

your green looks really stressed out .... not sure but looks like maybe overwatering... just a shame to see those plants so stressed... you got your ph right, right ?

hi, lights are about 1 meter high and they are fed with some universal hydroponic solution. ph ok.

I would flush them and put them out of direct light for 3 or 4 days.... it should get you back to scratch. If the ph is good then that should fix the problem, otherwise you have an odd problem, hope that helps...