The rule of thumb is that if the problem shows on the bottom, it's your needle tension. IF the problem shows on the top, it's the bobbin. So i would work with your top tension, rather than the bobbin.
Are the rats nests everywhere? when you start? on curves?
If it's on a start, you need to pull your bobbin thread up and hold both tails. If it's on a curve, this is a common problem, you're going a bit too fast.