Yep, the bottom tension was way off! Gahhhhh! Luckily, Bernina gives you the tools to keep your tension perfect. Here is a little gizmo that came with my machine. A tension checker/adjuster for the bobbin thread:
You snap your bobbin case with its threaded bobbin into the gauge, wind the thread around the little wheels, and gently pull on the thread. The red needle in the gauge will show you what the bobbin tension is. It SHOULD be around 220 for normal quilting. (I will probably have to experiment with it to get any cording tension to be perfect.) If the gauge reads something other than 220, you take a tiny screwdriver and turn the tension screw on the bobbin case, lefty loosey, righty tighty. Then pull the thread around the wheels again, and adjust as many times as necessary until it is 220 or close. Different thread weights may have a different "perfect" number, but at least you have a starting number, and can make adjustments accordingly. Also, every time you wind a new bobbin, you should check it in the gauge. You can adjust the top tension with a number in the display window of the Q-20, so between the 2 numbers, you should be able to get perfect tension every time. After having learned about tension from experimenting, I found this is true. I can get beautiful tension results every time now!