According to the recipe, I believe you don't add the whole packet, in order to alter strength. It states that if you have fine hair (I know that you don't), one should use only about 1/2 of the Knox. I am going to assume that, regardless of fine hair or not, you shouldn't use the whole packet.
It says that: "Use half the gelatin for a milder treatment or for shorter than shoulder-length hair."
Here is the link:
Pedaheh's Hair Blog: Science-y Hair Blog Recipes