Quick newbie CO2 question.

I have been putting my plants outside at night so that they get good CO2. Is this necessary? Temp is not an issue although as they get bigger privacy MIGHT be a problem. Am I better just putting a bottle with bicarbonate of soda inside my cab?
I should point out the window to my grow room is always open and there is a lot of flora and fauna right outside. Will this mean I don't need to put my plants outside?

Some pics of my seedlings today....

As long is there is circulating air the amount of CO2 remains constant, about 390 ppm. Moving them outside will do nothing to raise the PPM, to raise it to the ideal PPM (1500) you need to augment. The bicarbonate method is kinda weak and labor intensive, Grow stores usually carry compost bags that are good for 6 mos. and depending on your room size can raise the CO2 levels nicely.

plants want co2 during the day, o2 at nite.

Thinking this much about co2 is probably not going to be of any use to you right now in your grow. While co2 can have great results, it seems to be one of those additions to the grow that is only beneficial once all other variables have been tuned in.