Brewed my Belgian grand crew last night, pitched while labs wlp500 starter that I had made. It's in a 6.5 gal carboy and I was looking at it today and not much is happening, which isn't a big deal, may just be a big lag time, but I was looking at the airlock and I noticed the water is low, and I just filled it last night when I put it on. I watched it for a few mins and noticed it's sucking the water from the airlock to the carboy. Like there is low pressure in the carboy. So I popped the airlock off and put it back on, re-filling it and same thing. The atmospheric pressure difference between yesterday and today is not much so aside from that I have no idea why this is happening.