Well, they should not look like that. The brown part. The fuzzy part is good.
AN is a breed of it's own, just had a long problem / fix with that on another thread, ended up switching nutes to get his PH under control. Long story.
In general, you should not have staining on your roots. I have no idea where kelp extract falls into this or if it can stain, but I see that AN recommends it.
I wish there was a simple test for root rot other than a microscope, but it looks to me like the beginning stages, unless it is something in the water doing this. Got an old school microscope tucked away in a closet?
With
hydroguard, it takes time for the colony to build so protection is not immediate. Basically it is biological warfare, you want the good bacteria to get a foothold and starve off any comers. If you had pythium in the system at the same time as
hydroguard, usually pythium wins. From your title I surmise this is an ongoing problem for you? What are your procedures to clean up between grows?
What is the water source and starting PPM? This could be diatoms depending on your source.
If we can't nail this down, you might consider going sterile this run by adding H2O2 and stopping
hydroguard. This will kill the root rot immediately if that is what it is. I recommend a live system, but sometimes you gotta add H2O2 if you are confirmed root rot.