All plants getting sick - Over watering?

Hi,
I have a Panda Aeroponics running and today the plants show sickness. I've ruled out EC-problem and pH and I think the system drowns my roots.
The Panda aeroponics is a system where the pump runs 24/7 and the nozzles doesn't spray, rather sprinkle the roots. The iddea I have to save the plants is to connect a timer to the pump and give them air at least 50% of the tume (trying 30min on/30min off). Please see pictures of plants and roots - I welcome any tips.



EC: 2,1
pH: 5,9

Well, it all got worse and I had to kill the plants. Anyway, I'm starting a new batch and I could use some information about putting the water pump into a timer. I've seen many people adjusting the on/off differently. Mostly with watering off more than on (like 1 minute on, 5 minutes off and so on...). Why I'm hesitating to turn pump off (at whatever interval) is that this Panda Aeroponics from General Hydroponics is designed to run with the water pump on at all times.

My plants roots r always under water but lots if oxygen from flooming and water temps never above 70. Add air or cycling pump should do it but u have to keep temps low as well.