Maybe it's just the pics but your plants don't actually seem distressed. Other than the one pic with the burnt edges they look fairly healthy.
I was under the impression that you were measuring your TDS? Anyways you may be reading way too much into this. Don't worry though I understand completely. I can give people plant saving advice only to turn around and nearly destroy mine. When our product relies on how we handle and care for it we often times see things that aren't there or exaggerate the seriousness of what is there. It's because we're too close to the situation to be 100% rational. Don't stress it.
Also, you said your using 2 pots for 1 plant because the roots were growing through? @bob31 said being root bound can show those symptoms. If he's right then I wouldn't think it's a coincidence.
Sorry for the lengthy posts. I had a lot to say but was traveling and couldn't message