I've never had to deal with this, but I've heard others mention that they've wrapped their tanks with tight fitting Saran wrap type plastic, over the entire suface of their tanks when insecticides are sprayed, or they are doing major painting in their homes.
They got a powerful airpump at lfs, and a very long airline tubing to run from the tank - to an outdoor area far from the spraying.
Upwind would be best if possible. Place the airpump outside, and feed fresh air to your covered tank by slipping the open end of airline into a small hole in the plastic wrap near one edge of the the covered tank, and taping around this point. Then a few very small pin sized airholes in the plastic wrap ( or natural leak points ) will allow you to keep a positive air pressure on the tank, forcing air OUT of this enclosed area above the water surface, and hopefully keeping any insecticide vapors from entering the tank.
Under tank filtration may be a little trickier, but use your head - you'll figure out something.
Your aim obviously is to keep vapors out of any open exposed areas of sump/wet-dry as well. You may have to deal with this similar fashion - but could be slightly more difficult.
I would leave it this way for more than a half hour after spraying. If all goes well, and you constantly are feeding fresh vapor free air to the system, you could go for a much longer period of time.
QT's same thing unless you want to tear it down and just put back up later.
Watch your critters close -
Don't let the plastic wrap pop, it should be tight and bowed up some from outside air pressure -
You should be able to feel small stream of air coming out of these small pinholes in the plastic wrap -
Don't skimp on too cheap of an air pump -
Home Depot sells long lengths of vinyl airline tubing on those big spools, you can get it cut to length. Better than trying to splice a bunh of short lengths together from lfs.
Run some activated carbon or polyfilters if possible -
Reduce but do not eliminated surface water rippling by any powerheads you may have in place -
Keep your fingers crossed -
Wish you both luck !
