the tailpieces are not draining the pwt fast enough to prevent the water still standing from going anaerobic. the plants are drowning.
even though you have drilled the extra holes they only drain down to the point where the perched water table would normally exist in your medium.
can you pull the plant containers out one at a time and have someone run an ice pick or a piece of wire or something up the tailpieces, wallowing out the coco sort of?
i wish i were there. i don't understand why you are not draining.
how much water how often are you giving them?
D9 nailed it as usual. What coco are you using? Going to have to be some seriously course shit to keep from compacting over a cycle with that many feed cycles (the draining action creates a vacuum as you know, that not only exchanges gases, but will also compact a soft media like coco). Chow mix would fair much better if wanting to stick with coco and high feed rates, but screened turface or hydrotron is probably the best option for the direction you guys are headed with this system.