Help! Plants dying fast!! Light burn, nute burn, something else?

Can someone please help me figure out what's wrong with these plants? They are about 5-6 weeks old. The plant started out looking out like the one in the first pic with a little browning on the tops of the leaves- not the tips until later. Then it went downhill really quickly and looks like its gonna die- about three days after the symptoms first showed up. Now the top fan leaves are scorched looking and shriveling up.

I don't think it's nute burn bc I have only given them 1/4 strength houseplant fert a few times. I don't think it's burning from the lights because I only have 3 27watt CFLs and the plants are about 5" away from the light. WTF is wrong with them?
Thanks for your help!

-PN

flush, get your ph to at least 6,then transfer to a larger pot,then feed it regular strenght nutes.

thats phopphurs diff i had the same thing flush your plants and make sure you add enough of all your neuts N P and K and make sure you ph is balanced but only do half str neuts

JUST had the same exact problem my friend. Do what Kingofqueens said: Flush it with pH corrected water, let them recover a bit and then transplant them to bigger pots.