Planted Tank Guru
Join Date: Jun 2004
Location: Baton Rouge, LA
A biowheel is normally enough to ensure plenty of oxygen at night.
If you have time before your trip, you might try running the CO2 all night long, keep an eye on things, and see what happens. Chances are, unless you have the CO2 turned up beyond 30ppm and almost to the point of fish gasping, it'll be alright.
Otherwise, I'd do one of the following:
1) Put a cheap aerator and mechanical timer in to aerate the tank at night.
2) Turn off both CO2 and lights for the four days. Consider it a blackout, like the ones used to treat algae infestations. The plants may be set back a bit, but should quickly rebound.