The yellowing of the lower leaves is a sign of nitrogen deficiency or lockout. It's pulling nutrients from the lower leaves. If your ph has been stable I would slowly step up ppm and watch close. One of the pictures looks like the inner roots had root rot and the plant managed to pull through it so that's a good sign.
Hi, here's update.
Thanks to all you guys my plants were showing nice recovery. And I thought they were finally gonna be fine altogether.
This was taken 4 days ago. Still small plants but they were really starting to grow and the leaves had nice colors.
And its roots:
And 4 days later, this is today:
I LSTed only the main stem because these plants went through some serious stress from the beginning and I didn't want to cause another stress by topping them.
The roots are starting to grow really nicely, considering they had almost none just a week ago.
Now I encountered this problem:
Dynagro Foliage Pro @ 350 ppm with negligible amount of Protekt, Hydroguard, and sulfuric acid based pH-down.
After setting pH at 6.0, it drops down to 5.4 after 24 hours with decreased water volume. So I just add some tap water(7.3 pH) and pH returns to 5.8-6.0.
Ambient temp is 85~86F
Water temp is 66F with chiller running
RH is around 35%
Oversize air pump running at half power
I was gonna switch to 12/12 after 10 days, but if this stunts the plants again that can be later.
Regardless, I'm going to salvage these plants and see them bud no matter how small!!