I cut off the first set of true leaves last night before putting them to sleep and when I just woke them up I noticed that the yellowing had traveled up towards the second set of true leaves. I feed it 1/2 nutes for the first time from 1/4 strength and cal mag but my leaves are still turning yellow!
I had a similar problem with one of my auto's always drooping and doing the red/purple stem thing. In my case, the plant was hungry more on the Phosphorus side. Looks like yours may be along those lines with also an N def