Start with Sharon's suggestions.
It also looks like your top tension is wayyy loose. Do you have a Towa gauge for the bobbin? It will give you a numeric starting place to start balancing your tension. In other words, you don't have to go by feel to make sure your bottom tension is right. Different bobbins will run differently, as will different threads. I bought a box of 100 bobbins, and no two run exactly the same. By using the Towa gauge, I can adjust my tension so that I run the same tension despite different bobbins. A bobbin in the bobbin case will run different inside the machine (where the spring is engaged) than when it is outside the machine (where the spring is not engaged). The Towa mimics the bobbin case in the machine.
HTH!!