Adjusting tension when stippling

Question

Hello,

Thanks a lot for solving my problem with the presser foot. Now, do I disengage the feeddogs or not...Also, the top tension looks okay when set at 3 on Pfaff 7550, but back of the quilt doesn't...I see loops, should I adjust the bobbin tension, which I have never done before and if yes, can you tell me how...
Many thanks!