Change In Row Tension - All Rows Are NOT Equal
Did you know that almost every knitter's row tension can vary? For some the looser tension is on the knit stitch side and others it's the purl.
Often the tension variance is barely noticeable, but you may find yourself working with a fiber that causes this difference to be very apparent. I find it in my own work most often when I'm using fibers with lots of drape.
You could always, tighten up your stitching on your looser row, OR you could:
Change One Needle Tip!
This is a really easy fix. First decide what stitch row is looser and work that row with a smaller needle tip. Work a few rows then look at your work and notice the difference.
Interchangeable Needle: Merely replace one needle tip with a tip in a smaller size. Use that smaller tip as the working needle for the looser row.
Standard Circulars/Straight Needles: Circulars/ two sets . . . Straight needles/one of each size