Commercial setup - 4 rooms UC.

I need to use a couple bug bombs - havent used one in a year but I saw a roach yesterday and don;t want to see another.

I'm in between runs right now so the flower rooms are empty for a couple days - UC systems are running fresh water + UC Roots to wash clean right now.

When I use the bombs, should my UC modules be empty of water+UC roots, or filled with water, or does it even matter?