two plants sharing dwc one fine one turning copper?

One plant looks great the other is dieing it would seem from bottom up leaves are drying out and turning a copper bronze like color. http://s1.directupload.net/images/130220/rcpeb2dt.jpg. the other plant is only 11 inches tall with fan leaves bigger than my hands http://s7.directupload.net/images/130220/lh93whmw.jpg any ideas?

Are the roots of the big one choking the roots of the small one?

What's the PH,ppm ? I would cut the nutes in half, set the PH to 5.8, check for heat issues.Sleep for 2 days & check again. That's what I would do,you might want to wait on someone that didn't ride the short bus to school. I don't have a lot of experince.Peace