Splay leg chick pecking talons

[Rinnley]

my landlords chick is splay-legged and curl toed, he's responding well to a homemade brace and a healthy diet. he had mites, my landlord put diatimeceous (sp?) earth in the box. he's pecking his talons, is this a sign of mites? a vitamin deficiency? or is it that they'e grown b/c of his lack of mobility? should i trim them? should i take the brace off now?
i've made a little video of his brace and general condition. he is a little over a week now. This is my first time caring for a chick so any advice would be much appreciated! thank you!