Root rot is effectively caused by insufficient oxygen to the root zone. To treat it in a hydro set up (I am assuming you are in hydro) Get hold of some H2O2 (Hydrogen peroxide) and mix up some at the recommended strength (.5ml/l usually for 35% volume) If Flood & drain, drippers & tubs or NFT use this solution for 1 flood. Discard used solution and repeat following day, water by hand if needed with ph'd water. Repeat the following day. The next day, go back to your usual feed/water but reduce the frequency of floods/feedings (max 3 x 15 mins daily). If in DWC/RDWC, flush through two days running with same strength solution of H2O2. On day 3, go back to regular feeds but increase amount of air being pumped in and reduce the level of the water to allow more air into the roots. The top of the buckets should look like boiling water. Hope this helps, it has worked well for me in the past. Peace W