Right up front, I know nothing about DWC so I can't give you any specifics for how to correct the problem - but what I see in the leaves is two-fold... too much nitrogen (very dark green leaves) and a calcium deficiency (yellowing leaves, veins green). The ONLY thing I know about DWC is that the ideal pH is around 5.8...
I'll let other chime in here for more specifics.
Good luck!