I'm hoping someone with experience using Coco will chime in here, but I'm wondering if these plant's aren't being over-watered. You're using a Coco/Soil mix right? If the roots are kept constantly saturated they may not get enough oxygen with this constant yet slow flow of water/nutrients. It seems like most of the Coco grows I've read water once each day, giving the medium enough time to dry sufficiently between waterings. If yours is Coco with soil mixed in, then it is going to hold moisture longer. Again, I have no experience with this medium, I've only done Ebb&Flow with Rockwool and Pea gravel and organic soil grow - in soil I water around once a week.

Again, I've never played with this stuff so I'm just extrapolating from what I've read - hopefully someone else will chime in here.