seedlings under 12/12

hey i put 4 seedlings in my tent under a 400 hps. the tent is already flowering, going on week 6, i thought hey i might be able to get like another ounce off these 4 seedlings, if their fem. but now they've been in for about a week, and 2 of them have lost their chlorophyll. the little sucker/ cotlydon leaves are yellow, dont have a cam right now. shit i know it makes things alot easier to help if i have pics... they just have the second set of true leaves showing, but they are yellow as well, lights are way above them, so i know its not burning, not getting any nutes, just water, cause they arenty 2 weeks old yet.
any help as to what would cause seedlings to yellow under a 12/12 light schedule.
the ph of the water is around 6-6.5

these 2 are fine, but are same size as the yellowed ones, just picture these yellow. each are in 2 liter bottles, painted and all that. if they die im not thta disapointed, dont expect anything from them anyways.

i tried an experiment with this before, but i used 22 mid seeds. most ended up stretching waaayyyy too much and fell over with the smallest stem ever. i got one good one off it but she took over 18 weeks, so i just chopped early, still curing, but got about a quarter off it. i grow in hydro so im not much help with the yellowing. id just make sure the light isnt 3' away like i did.

no the light is 14 in above the other flowering plants, just have these sitting on a milk crate in the tent cause i had the extra room.