Can anyone identify this ?

How's it going everyone!
Hope all is well.
Recently notice my leaf started to burn. But my nutrients isnt high. Didn't have any issue before. Possible stain differences?
Been spraying neem, pass few day due to mildew.
Could it be Potassium Deficiency?
Thanks for your time !
Any input would be great!

Setup info
2 double ends
SFV OG
DAY 10 FLOWER
Drip to waste
A&B advance
Cal mag
Bud candy
Kool bloom
PPM 1100-1200, started at 900 first week.
PH pen when out. Guessing 6.3-6.8 range

they look like they're nute burned...badly.
and overwatered....badly.
if the rest of your plants are in the same conditions and look good, check the roots on the ones that look bad, see if they look healthy, see if there's any bad odor

Agreed with Roger here. Your PPM is very high. Very high and it shows.

You say DTW - is this on coco or what?

It is in hugo cubes 6 by 6. The bad ones, cubes are pretty light white roots. No funny smelly. I am currently going to flush it out just in case . Here some picture update. Some dark discoloring around the edges ?Just have not see anything like this happen.. Possible to much ppm

Thanks for your time guys