Too much water, both roots and leaves. Best is to start over mate. There's a coupla very good hydro tutorials in the hydro section, go read a few and then try again.
With hydroponic growing you can't 'wing it'. If you want to grow your plants in net pots with expanded clay try DWC. Even there your pots are just above the water not IN it, it was my biggest mistake starting out too is over-watering. But all-in-all that's full-on drowning happening right there.
It'll be faster starting over and trying to do better that attempting to save these, trust me, been there and it's not worth it.
