the trick to making sure your machine is in correct tension balance is to sew a line on the bias of fabric and then gently pull the fabric holding ends of stitching. If the tension is in correct balance then the stitching should not break. If one side breaks then that is the tension that is too tight and needs to be adjusted . I do not adjust my bobbing tension. but only the top. Also I have found that I do not need to adjust the tension when FMQ . I use invisible thread on the top and thread matching backing on bobbin UNLESS the bobbin thread is too dark for the top and few of the stitchs show thru. EG- black thread shows thru on gold top.