Why not just remove the tube from the bottle (or just uncap it) and let the CO2 escape for a few days? No point in adding CO2 to the tank if it's not going to be used.
That little of an amount should be fine unless you're on a very aggressive yeast/sugar mix.
My mix runs all on its own through 2 diffusers and I've got 4 2-liters running on an 11-14 day mixture on my 55. Runs all day and all night and my PH is right around 7.3 or so.