Roosters don't need the extra calcium from shells really. But if they really think they need it, they'll actually eat alittle bit. But it's hardly ever.
Feed him only his feed, no extras.
There's no need to use separate feed, for different genders as long as everyone isn't fed Layer...
Cut out all treats, & why are you giving him shells?
Hens, & roosters can be fed one diet, Chick feed, Flock Raiser, or All Flock for all genders, & ages. The only thing that would have to be supplemented is calcium(Oyster Shells)which can be fed in a separate container, or feeder for the hens...