Stuart6060, Have you upgraded to the BIGGER lights yet??
I'd put money on it that it would grow alot better under higher watts, maby a 150 HPS.
How close are the lights to the plant ??
Right side up the plant potter for a week, until the roots are deeper in the pot.
Let gravity work for you for a week, to help it get some decent legs.
Then throw that sucker back upside-down and let it grow.
I bet this method increases growth substantially.
PEACE !!