Brewed a 1.080ish beer last night. Maris otter, with a little C75, and black patent. Mashed at 150-149. Made a 2L starter, and pitched at 6PM. Aerated with pure O2 for 45 seconds about 5 minutes later. 5 gallon batch into a 6.5 gallon carboy that is sitting in a bucket of water at about 67-68 degrees. Went to check on the beer this morning at 9 and the top had blown off. Any thoughts as to what could have done this? Should I just use a blow off tube for big beers in general? This isn't the first big beer I've made, but the first blow off I have had.