There is apparently a very beneficial soil bacterium out there called Streptomyces Griseoviridis. I heard it could prevent root rot in orchids while providing nourishment and better growth. It is not, however known to treat the rot and used only with the healthy plants. Since the bacterium is occurring in nature its use does not contaminate water and supposed to be environmentally safe.
A few commercial products contain the bacteria.
Did anyone here try it before?