Is this Nitrogen toxicity / overwater / or something else? (DWC)

Lower the pH value to 5.6, Rum might help.

the other plants dont really look healthy either. from what i can see in the pictures. stems color is unusual. and they look stretched and leafs hangin. theres an imbalance. some are more resistant maybe. are those autos? and whats your ec?

I think this is about the balance of nutrients causing more uptake of one thing and not enough of another not necessary a large excess. No root rot is good, but how are the roots looking. are they getting enough oxygen

Think 010001000011 made typo, it should be 1200-1300 ppm. Btw, mulders scale/scale ( google this ) here is obvious, excessive Nitrogen blocks absorbtion of Magnesium, you have big troubles with Mg deficiency and N toxicity. Plus you are in Thailand, i heard its very complicated to grow, because of high temps and humidity.

Waaaaaaaaaaaay waaaaaaaaaaaaay over fed! None are healthy, despite what you may think................. Anything you change will take about 2 weeks to show results in the leaves, it is not do a flush, then hope to see a difference in 2-3 days.

Over fed 1 million %.. it is brave

Not all plants can handle same levels of nutes.. though it should be a fairly small band for vast majority. 120-130ppm is usually near the high end in vege phase... definitely need less in flower. If you are drastically higher than that, consider reformulating a bit.... if you are already around that level, consider diluting what goes into the ones having issues. if it's a one-tank-for-all context, becareful of compensating for th eminority, but finding something that keeps them all happy may be worth it... i just wouldn't cause problems on 90% of your grow to help 10% of plants with oddities, etc... consider other optiosn too... is the water clean and properlymaintained / refreshed as needed? problems in veins often relates to rootzone or water quality issues. Again, some planys may be more robust than others... check out jacks nutrients 3-2-1 steup.. find some ppm tables... mimic that. I'd suggest about 10-15% lower than their instructions to start. Compare balance/ratio to what you are providing and maybe something stands out in regard to these symptoms...

Growmie, before you start throwing more stuff at her, check your EC/PPM and reservoir temp Dark + clawing leaves definitely could point toward too much N, but together with the purple stems, stalled growth and dying lowers, I'd be looking at root-zone / nutrient uptake stress first. And “same feed, other plants are happy” unfortunately doesn't completely rule it out, this girl might just not be taking it up properly. Have a proper look at those roots too. No funky smell is a good sign, but I'd still want to see healthy, firm roots. I also wouldn't keep flushing her with plain water. I'd get her back onto a mild balanced feed, plenty of bubbles, stable pH, then watch what the EC does over the next day or two. Drop your EC/PPM + water temp, those two numbers would help a LOT here.

You start operation of at least 53 girls and can't read them ? Brave ;))) Ill leave to dwc growers this one. They look overfed and sick, most probably toxicities and lockouts.