Need a root diagnosis

It seems to me that it's rot. The texture looks soft and slimy. If that's the case, it's rot. I would try to cut off the ugly parts. But it's no guarantee of anything. And maybe some treatment with a product containing cellulase enzymes like Sensi Zym or Pure Zym. It would be important to identify the source to prevent it from coming back. And clean everything with water mixed with hydrogen peroxide. Good luck!

Hi mate, looks like not enough oxygen is getting absorbed by the roots. I'm sure you're running an air stone so I can only assume its your water temp. Too not and the roots can't absorb it. Too cold and they can't absorb nutrients. I'd say your water was too hot, greater than 72'F. I hope this helps, good luck and happy growing

Half hydrogen peroxide 3 percent, and half water at righ ph mixed will kill root rot and is safe for plant. Only on roots. Do not get on leaves.