For quilting in the bobbin I use Bottom Line in a light silver color and it is almost invisible, no problems with the bobbin but it will not work on the top. However it is so fine a bobbin will last twice as long. It seems to blend right into any color and virtually disappears into the quilting on the back. May be the problem is that the thread you are using was never meant to go into the bobbin but only be used on the top.