I dont' have a Designer I but this is what I do when I have tension trouble. I usually use a straight seam.
Each time you make a run, write down which tension setting the machine was on, Look at it, evaluate the stitch, turn the setting one space, write down setting. make the run of stitches, look at it, evaluate.....is it getting better or worst. If work move the other direction. You will find the correct setting but it will take time.