Quote Originally Posted by SpaceNeedle
PRECISELY!!!
The cube will never get a chance to dry out, and the plant will develop root rot!
Let me repeat myself....the cube is NOT SUPPOSED TO DRY OUT!!! It doesn't need to - not in a DWC, anyway. Air is circulated through the reservoir with one or more air stones, disolving oxygen into the nutrient solution. The plants get all the oxygen then need from the solution.

And being wet isn't what causes root rot in a DWC system either. Usually root rot in a DWC is caused by res temps that are too warm; insufficient air flow into the res; or roots that grow too thick and restrict water circulation. Failure to completely clean your system between grows can also cause root rot as well as other diseases. But not letting your rockwool dry won't do it.