I see videos n pics of rd's wit the humps on their heads but mine hasnt grown one yet. Its about 9in now how do i get the hump to start growin or that just some that comes naturally.
It depends on genetics mostly. It will also depend on the sex of the fish, generally the males get a larger head than females. I'm not aware of any magic foods that produce the nauchal hump. Either you got it....or you don't.
i would venture to say that if by 9" there is no hump at all on your RD head, its a good bet its a female.
if it is a male, as was said, alot of it is genetics. the best way to get it to grow would be keeping the fish as healthy as possible....clean water, and a good, varied diet.