Hi CQ,
I am assuming you are machine quilting with a domestic sewing machine (as opposed to a long or mid arm set up).
Thread comes in varying weights and to further confuse us the higher the number the lighter the thread. You can MQ with different thread weights in top and bobbin but as you discoved it involves adjusting your tension. Sometimes just the top but ofter will require bobbin adjustment as well. I recommend getting your hands on one of two excellent machine quilting books that explains the difference between threads and have pictures that show the difference seen when using different threads. The books are Harriett Hargraves Heirloom Machine quilting and the other is by Diane Gaudinski, title Guide to Machine quilting or something like that. Most thread marketed as "quilting" thread is 30 wt. Most all purpose threads, used in piecing is 50 wt. If you want to experiment on your own, I recommend getting a 30 wt thread and loading it both on your bobbin and on top and give it a shot. Just make sure the thread you get doesn't state it is for handquilting as many of these are coated and could mess up your machine. There are tons of manufacturers. Superior threads make beautiful threads in lots of colors and weights.