Not Nutrient Burn

Giving that medium too much water looks to be drowning it

Your roots look like they are starting to rot. Sterilize your hands and then feel the roots. They should not be slimey at all. If they are slippery then you got rot starting. H202(4%) 2ml/L added to your mix should kill off any rot. Good luck.

You can still burn at 600PPM its not unheard of. Try some Maxigro with your Maxibloom or in place of, its more for the vegging side of things. The micro monkey additive will help it uptake more p and k in theory. Good Luck!

She's just getting the wrong type of nutes and it's really messing her up. General Hydroponics makes a great line (I use them myself in DWC) but you need to give them at least grow nutes when in veg and bloom nutes when they start to go into flower. I use the Flora series, just the 3 part with a few adds ... Start feeding her for the stage she's in... Get some Flora Grow, Flora Micro and Flora Bloom - dosages are right on the label.... easy peasy... I'm also thinking your ppm is a little low for her age... but if you add some Grow to the mix, it should get to where it needs to be... Good luck!

I also did not understand the problem here till I looked at your nutrients. You do not use any growing nutrients with Nitrogen (N). During the growing and pre-flowering phase cannabis needs a lot of Nitrogen (N) for growing. You are just feeding her phosphorus (P) and potassium (K). She needs that too but mainly after the pre-flowering phase to develop buds.