First set of true leaves yellowing and dying. Not cotyledons! Help please!

Hey guys. My first set of true leaves look like they're dying. Started with yellow tips from what I think was heat stress and adding nutes too early under an hps. Then switched back to pH water under a 55 watt cfl for a couple days and started to see new growth. Figured it'd be OK to go back to the hps yesterday and kept seeing the new growth come out green and pretty but the first two leaves are getting worse and worse. I heard sometimes the first two die as well as the cotyledons. Is that true?
I'm growing in dwc 5 gallon buckets in hydroton. PH 5.5 and good room temps. Plant is about 17 days from seed with 1/4 strength GH nutes.
Like I said. Other than the first true leaves everything else is looking good.
I'll post pictures in a bit.
Thanks for any help.

might be root rot! how is the root looking? pic?

it only has one root. it's the first one from the seed. looks white and healthy just really small. it poked out of the root cube and grew awesomely for a few days straight into the res. after a few more days of slow growth and no more roots. i moved the hydroton to find there were a few small roots and probably killed them in the process of re planting them in the media because when i checked back they looked brown. so basically it looks as if the plant has one root to it. any idea of how to get more to sprout? it might just be a lost cause as i've messed with it a bit. but i'm still going to give it it's due time to see what develops. i do know that it is growing and showing new growth daily. slow. but i can see it. i added a picture to my first post. also. i'm getting what looks to be foamy soap bubbles at the top of my res every few days. don't know what that is either. any ideas on that one?

So after some reading and hearing the foam is bad I took out all the hydroton and washed that as well as doing a full pH adjusted res change. The water was kind of starting to smell a bit so I felt it was best. As I was changing the hydroton I also noticed new root growth on the plug as well. Good sign I'm hoping. I also planted it a bit deeper this time hoping some of the new roots will hit water faster. Hope it works. Maybe the old leaves will die but at least seeing new growth on bottom and top gives me a little hope left for this one!