In the past my protocol has been as follows when painting entire rooms:1) Leave any closed systems such as canister filters running, they won't pull anything in.2) Cover the entire aquarium with a sheet, or painters plastic, this will provide a mild barrier against big stuff. Be careful that you don't seal off any cooling air inlets/outlets on lights.3) Take an air pump (the sort you would use with an airstone). Put it far enough away that it will draw fresh air (outside is good), and run that into the tank. With a huge or high value tank tank I would consider a box fan and flexible dryer ducting.4) Run carbon if you are nervous.5) While I might point powerheads and return pump outlets away from the surface I advise against killing all flow. Sure that will cut down on air exchange, but a reef with zero flow for more than a couple hours can be an unhappy place.Not at all scientific, but it has worked for me. As to how significant the risk is to begin with I'm not sure, but I've never wanted to find out.On a related note, whenever I set up on a hard floor I always put felt feet/pads on my stands before initial setup so that I can slide the tanks a bit to get them away from the wall. The biggest tank I've done this on is an 8' 300 gallon and it's saved me several times