Alright, brewed my first batch this past Saturday. Didn't have any issues, followed all sanitation procedures. My beer is in a 5 galloon plastic carboy. I have setup a blow off tub running into a growler of sanitized water. The blowoff tube/growler started bubbling pretty aggressively after about 12-18 hours and bubbled all day yesterday. I woke up this morning and it had stopped bubbling completely. There was a very large "head" at the top of the beer while it was bubbling but now that has disappeared since the bubbling has stopped. I placed a fermometer on the side of the carboy and it is reading 70-72 degrees. Should I be worried? Is this normal? I assumed that it would bubble until it was done fermenting? Help.