I've had my brew in the primary for around 24 hours and the liquid in my airlock dried up to a point that there wasn't any more bubble, but just air escaping above the liquid. I figured it out after staring at the bucket for a few hours and willing my fermentation to restart (that works right?). I topped it off and I can now see the bubbles again. Is this a common occurrence? If so, how often do you top it off to keep it from happening? Below is a picture of the airlock I'm using. Also, I had it filled with Vodka upon the recommendation of some older threads.