Rot Root? whats wrong with this plant?

[Hashashin]

A week ago I noticed a foul smell coming from the water in my DWC plants. I changed the water and even rinsed the roots gently.

It seems as though this one suffered more than the others but I'm not sure what from.

Is it root rot? If so, how do I fix it?

If not...what's wrong?

here are pics of the plants.


the middle plant is the one with the problem:
Root Rot? - 420 Magazine Photo Gallery

this is the roots of the problematic one:
Root Rot? - 420 Magazine Photo Gallery

this is roots of the one in the back left:
Root Rot? - 420 Magazine Photo Gallery