I started a batch of hefeweizen in the fermenter sunday evening and i attached a blow-off tube. I got a rather heavy blow-off over monday and tuesday, so on wednesday I replaced the blow-off tube with a regular air lock. The air lock was bubbling once every 20 or 30 seconds. I checked on it again this afternoon (friday) and the lid was about to blow off of the bucket because the airlock was stopped up again. I have never had this happen before. I cleaned out the air lock and put it back on the bucket... Is that uncommon?