When you foiler feed 2-3 times per week is it during light hours ? It should be at dark.
I never foiler feed till recently and I killed everything, about 20. Only did it a few times and things looked great. Then bam all started to turn just like yours.

Also had a cold blast on hydro water and they turned yellow almost over night.

The other thing is ventilation ? Are the getting fresh air or just push around air ?

Your not getting them enough water most likely. Do the ebb and flow or you could drip back to rez But they need more water. I run drip 130gph pump wide open on 6 plants 24/7. Those rocks do not hold water like hydrtron or all rockwool.