I had root rot really bad and did alot of reading, I gently pulled the dead rots off the plant (black roots) and sprayed the roots and medium with a 50/50 mix of peroxide and water let it set for about 5-10 mins and then put it back where it was with new water change but with about 25% nute strength or if it has nute lockout then just ph'd water. I was running DWC and the plants responded well to that method ( I used many other methods like mixing peroxide in the rez at around 10 ml a gallon but it didnt help). I believe pulling the dead roots off helps a lot. I didn't really have roots when I was done pulling all the dead junk off and they still grew back. Nothing is going to work permanently unless you figure out what is causing the root rot to begin with though. What system are you running, what is the rez temps, PH, and nutes used? This is very important stuff to mention when posting, it will help greatly when people respond and save valuable time when your plants are hurting. SM90 also works great with root rot and getting it under control. It also works as a preventative but it pretty much sterilizes the rez so it also kills the good microbes too. If you just can't get the temps in the rez where you want them then SM90 is great in my experience. Like I said though find the root of the problem (pun intended) and you will be able to fix the problem for now and later!