I do FMQ all the time on both my Janome 6260 and my Janome Horizon 7700 and have never used the "blue dot" bobbin case. I thought it was just for decorator threads that were too thick to feed through a normal bobbin??
Have the tension spring on the bobbin case checked - it may have gotten a thread caught in it and either plugged it or bent it to a point where there is no tension in it anymore no matter how much you tighten down the screw.
If it were me, I'd start with a complete new set of thread - same on top and bottom and loosen both top and bottom tension right off. Then slowly tighten the bottom until it holds the thread to the bottom but not to the point of eyelashes. Then tighten up the top until the stitch is balanced in the fabric. Make sure that when you're threading the top you have the pressor foot up so the tension discs are open, AND do the same when ever you change the top tension.
Good luck.