One day I was at a PetCo where they have one of the largest selections of fish food products, and I decided to check the ingredients on the backs of many of the containers. Not surprisingly, the overwhelming majority---including the Tetra brand flakes that I had previously been using---listed some sort of filler such as "fish meal" (which, for all I know, could be mashed-up brains, guts, and scales) as the first ingredient.
Then I came across Ocean Nutrition brand 'Cichlid Omni Formula,' which starts off by listing a wide assortment of natural ingredients (salmon fillets, plankton, squid, salmon eggs, krill, sea clams, kelp, herring, adult brine shrimp, and brine shrimp naupli)...and the list goes on.
It was a little bit more expensive, but well worth it IMO.
Fish go crazy for it, and I suspect that they're healthier as a result. There is also a 'Brine Shrimp Plus' formula of the same brand that I feed them as well. Both of these are in flake form. When I'm not feeding these, I feed mostly frozen bloodworms and, on occasion, frozen beefheart. Sinking shrimp pellets and algae wafers are also included here and there.
Just remember that whatever you are feeding your fish should be tailored to their specific needs. Wouldn't make much sense to offer daily bloodworm feedings to a predominantly herbivorous fish, for example, and it could do a lot more harm than good. Same thing goes with tossing veggie flakes and algae wafers at carnivorous fish all the time---just isn't in the best interests of the fish.
Anyway, that's the long-winded rundown of my take on the whole fish food topic.
BV