Variety is best. I feed my FH a mixture of Ching Mix Premium Staple, Sp100 HB, Sp100 Maxima, Hikari Gold, Bio-Gold, Aro Sticks, FDK, and FBW and market shrimp as weekly treats.
For Kok, it will depend on the genes of the FH, low quality will not develop much of a water kok, more of a hard kok.