Use "Roots Excelurator" by House and Garden, kills root rot and enhances root growth! Expensive but potent at 5ml/5gal's! Use it and watch it work.
I have been using that since the girls were babies. 1 ml a gallon. It has proven useful in the past but whatever is hurting my roots is not being helped enough by the Roots Excel. Thanks for the tip though, its good stuff.