Slow starter = bacteria got off the wrong side of the bed today?
Today is my 8th day of nurturing the sourdough starter. I noticed that after today's feeding, it seems sluggish. The only thing I did differently from the other days is that I used a handheld mixer to whisk in air for about 3 minutes on highspeed. It was just for fun. Besides, the formula I'm using (from River Cottage Bread Book) does say that once in a while, the starter needs a good whisking of air.
Is it normal for the starter, from time to time, be a bit sluggish?