It wont harm anything for one.
Two, if you want to help prevent it you need to keep ALL light out of the Res and or and clear pipes and or the rock wool in your case.
I'd say go to Wal-Mart and buy a black storage tub with a lid. This will give you plastic to work with.
Now cut either circles or squares big enough to cover your rock wool / top of entire container. Now Cut a slot into the circle/square which ever you
choose is best until you get to the center. Now in the center of the plastic cut a circle out bigger than your stalk but not 2 inches bigger or anything.
You can always cut the center hole bigger as she grows. This will block out your light and help with your problem I hope.