Hi Ed, the problem with that approach is that the bark as a medium requires frequent watering, and if you do that, then the roots in the rockwool will rot. Better to dig away as much of the rockwool as you can if you want to switch to bark. I too prefer the bark, as frequent watering keeps that brown fungus at bay. The EYOF always use rockwool for their phrags, so it is a constant challenge this..!