Slip first stitch of each row purlwise with yarn in front for ease of picking up stitches. At last row of each triangle, slip 1 stitch purlwise with yarn in front, move yarn to back and slip stitch back to left needle then k2tog tbl and place last stitch on a locking marker. Working with four balls means a bit of juggling but only 8 ends to weave in. The held stitch counts as the first picked up stitch for the next triangle.

To stop the tangling of the unused balls, thread them onto the cable and they turn as you turn your work and no tangles in sight!