Still new to the terminology, so you'll have to bear with us. ppm reading? Is that like the ph reading?
Regardless, system has been flushed and went back to 1/4 of nutes. Everything was fine until we tried boosting it up to half. When you mentioned them being underwatered, that made sense. We had the pump on a timer to water periodically, but why do that when the roots are swimming in water 24/7? I just now put the pump back on constant and we'll see how they look in the morning.
The plant with the nute burns doesn't look like she's getting any better, but no worse. How long would it take her to recover?