Help omg what happened to my roots?!!!!!

OK so I got some new nutes for my plant from GH and did a res change in my 5 gal DWC last night. my roots were in excellent shape before, they were white and long beautiful. So PLEASE PLEASE PLEASE help. i'm new to hydro DWC so any and all advice is appreciated soon. THANKS ALL WITH INFO.(AND ALL WITH QUESTIONS)
oH P.S.
My res temp dropped last night because it got ridiculously cold and I didn't really know how to bring it up.

Thi is called root rot, I got this once and 6/8 plants died (this is my diagnostics)

My advice is:

Set pH to 6.2 and change the water and nutes, set them very low EC 0,8 @.64 and put an aquarium heater down there and an airstone connected to a small airpump.
You should also hose your roots with clean water every day (no need to change your water tho)

root rot, your fucked sorry mate. make sure you sterilise everything, that shit will hang around for years.

Nah not for years... when I had it I just cleaned everything with antibacterial dishsoap and 2 survived ... you can find my thread here...

but you should quarantine each one in it's own water supply so if one recovers, it doesn't get infected by one who will not recover.