Let's see a pic if the roots... and start from scratch. It's not lack of o2 they are far to small to deplete it to a level that would cause issues.
Water temp?
Air temos day/night?
Circulation fans?
Source water?
Nutrients used and any additives?
Humidity day and night?
Are you running live or sterile?
Ph and ph drift over 24 hrs?
Pics of the roots?
Temps are pretty consistent,
water is around 70
Air 72 ish
I have a 12" fan on low oscillating and an air exchange that was set to do a complete turnover 13 times a min
Source is ro at 0ppm
Humidity is consistent 45 to 50
Running souther ag fungicide at .5ml per 10 gallons
Ph drift is minimal at .1 to.15 per day
250 watt mh they are getting about 13k lux now with the height they've put on
I've over watered plants before and this looks like its exhibiting the same symptoms.
At first it was just the bottom leaves but it seems to be traveling up the plant.