i've heard of it but i'm not sure where to get it. you could try pedia lite too. might help. is the foot curled? i know some people make a "shoe" to help that. i haven't had to tho. i'm sure that if you got the eggs from someone here that has a good rep that the problem isn't from breeding but...
i had two late hatchers that has started to zip. one was farther along but stopped. i have told myself that i wasn't going to help but i had to try. it had it's intestines on the outside of it's body so i had to cull. my first hatch i helped a couple and 2 did really well and 2 did not and died...