A bit more info would help and some pic's . However I can tell you the great majority will tell you rockwool sucks and is not used much. It holds too much water around the root ball and causes rot. Are you growing hydro ? If so post in the hydro with more info there are some great minds there. sounds like too much water. Some use rockwool and don't have prob's with ebb and flow systems you just have to keep cleaning under them to keep the slime down