Hi there,forgive me because i did not read the entire thread being so long and all but i thought i might be able to help a little, i think the plants locked out because those ppms are just to high and you seem to have gotten yourself into a bit of a mess ,don't get me wrong I'm a beginner as well but probably more qualified than some simply because I have only freshly had all these issues and worked through them recently haha :s.
I think you may need to: once again empty the res i know it sucks and it gets expensive.
Drop those ppms right down to a safe level.my auto ultimate is on about 1.3ec (700ish ppms) quite happily and eats down to about 300 ppm by change day. (this is a large auto in full bloom) I would perhaps start yours at maybe 400ppms and work up once shes healed.
I top up with Cal-mag half way through and just give plain PH water dayly. I never top up with nutes (sometimes il add extra overdrive in bloom and extra voodoo in seedling that's all) as not to throw the balance out it keeps my head clear of nonsense and numbers and saves me nutes.
Don't think u can push them by taking nutes to the limit it dosnt work that way "less is always more in DWC", they simply take what's needed from the bucket regardless of whats in there ,it will still suck it up in the plants normal syphon action however will simply burn when the mix is to hot.
We all have our own way of doing things,i recently spoke to someone that consider's themselves a master grower but fails to follow almost all rules set out by others ,I dont agree or disagree hahaha but just keep it real to what I know to be true and keep an ear to the floor.
I hope this helps mate any questions that a noob can answer hit me up I'm a pretty good noob
. GL
