Wife bought me a 2 stage kit and all of the perrifs, but there were no instructions so I began reading and consulting with another brrew friend out of state. I have a brown ale cooking for 3 days primary, and realized that I did not fill the air lock with fluid. I put some in today, but wonder if this is too late now? I am guessing that there is more venting out than could get in, but words from the wise are welcome!! . . . ??
It will most likely be okay. Like you said, there is more CO2 venting out, than air getting in, and the CO2 is heavier than air and will sink down to blanket the beer.