Discus are really no different than a lot of other South American cichlids. They appreciate a wide variety of foods. If you feed too much of one thing, they'll get spoiled and sometimes refuse other foods. Keep the diet varied.
I use frozen beefheart, frozen Hikari bloodworms, freeze-dried blackworms (I used to use live blackworms, but they were a PITA to rinse and keep alive, and the freeze-dried ones are just as good), ONF1 and ONF2 flakes, Hikari cichlid pellets/granules, frozen mysis shrimp (thaw in a net and rinse under water to get the oils off of them or you'll have a mess in the tank!)... the list goes on.
Basically, if they'll eat it, give it to them. High protein foods are good for younger fish to achieve good growth, but they do appreciate some veggie matter. A lot of people mix veggies like spinach into their beefheart, but you can also feed them veggie flakes like ONF2.
I use frozen beefheart, frozen Hikari bloodworms, freeze-dried blackworms (I used to use live blackworms, but they were a PITA to rinse and keep alive, and the freeze-dried ones are just as good), ONF1 and ONF2 flakes, Hikari cichlid pellets/granules, frozen mysis shrimp (thaw in a net and rinse under water to get the oils off of them or you'll have a mess in the tank!)... the list goes on.
Basically, if they'll eat it, give it to them. High protein foods are good for younger fish to achieve good growth, but they do appreciate some veggie matter. A lot of people mix veggies like spinach into their beefheart, but you can also feed them veggie flakes like ONF2.