Questions often come up regarding the bobbin holders (case) on Janome sewing machines. If you plan to do bobbin work, purchasing an extra bobbin holder with low-tension may work for you. The blue dot bobbin holder works well. It is already set for lower tension. This bobbin holder is used for free motion quilting. Make sure you mark this bobbin holder clearly so you do not use it by mistake for your free motion quilting. By having the extra bobbin holder you can adjust the tension further as needed for your bobbin work.
Click here for more information on Janome bobbin holders. Bobbin Holders 101 by Nancy Fiedler