If you use organic nutrients you might notice a slight browning to the root after feeding. If that is what you noticed we would say that it could be caused by the nutrients, however it could still be beginning stages of root rot. For treatment of root rot you would use a 35 % food grade Hydrogen Peroxide at a 1 oz per gallon ratio. For prevention of root rot try to not over water & you can use 35% hydrogen peroxide at a 2 teaspoon per gallon ratio to help add oxygen to the water & kill harmful bacteria. Keep in mind hydrogen peroxide will kill all bacteria, it does not care if it is beneficial or harmful bacteria. Once you mix Hydrogen Peroxide with the water it will start to break down. Hydrogen peroxide completely breaks down in 24 hours. Any damage to the root system will not only hurt your yield but it will make your plants more susceptible to diseases that can destroy your entire crop.