Yellow leaves with green veins, help please - PIC

5 weeks old hydroponics, went like this after I put in 1/2 strength Fox Farm nutes. Didn't seem to mind 1/4 strength at all, but now this... is this a sign of too much nutrients or too little? I have them in plain ph'd water right now until I can get some advice

its hungry for nitrogen. Whats the npk of the nutrients your using?

It looks like it's developing roots and it is canibalizing that fan leaf to do it.