You’re looking for biotin, copper and zinc. Amino acids are also helpful (lysine, methionine, threonine, etc.) But Leslie is right. If he isn’t being fed quality, he could be missing out on those things in his hay and feed!
I love Smartpak for their comparison chart (among other things!) You can compare all their hoof supplements and find a great middle ground on the amount of ingredients you want and the price. (But I personally love Smarthoof!)
Just to reiterate what Leslie said, you have to give it time to work! You should be able to see a difference in his frog sooner, but the new hoof wall won’t reach the ground for some time!