This is our first try at at all grain. We used the Wyeast strain with activator 3944. We mashed and sparged 9lbs and 12 oz. of grain with 1 lb of rice hulls to get 6 gallons of wort. Boiled for one hour with additional hops, cracked coriander seeds and dried orange peel. Total volume at end of boil 5 gallons. OG 1048. Cooled down and pitched yeast on Monday early morning 4 o clock. It went right to work. Question is the fermentation seems to be done already by Wed. morning. The primary is 6 1/2 gal. bucket with airlock. Initially lots of bubbling. Now nothing. Is it normal for fermentation to be so quick? It is in our closet at 67-69 degrees. Also we accidently put some pure oxygen in while still a little hot. Did we ruin?