I use C-lon for tubular herringbone and have no problems with the tension. I think it is also something you learn by doing it. First I had the same problem but now it's ok.
When i add a new thread, i first go down for about 3 to 4 rows in the next bead, and again in the bead next to this one, i go up with the new thread. Afterwards I knot and hide those threads and give them a little bit of glue.
To become a very good form in your necklace, I insert a rubber cord into the tube. You can also use a velours tube inside.
If you put these into your necklace from the beginning, it is very easy to become a regular necklace.
I hope this is clear for you, but if you have questions, just ask me.
Rita