Chow_13answered grow question 2 years ago I don't think you can really do much. I am assuming below that is just open space for the roots to mingle with each other.
I would cut out the square around where the rock wool is to at least get that out of there. Then cover the hole.
You are using synthetic nutrients so if you do run into any problems you can at least sterilize your solution with hydrogen peroxide.
Good luck and Happy Growing.