Yeah, you're on the right track if you can get them to try any new foods. I mixed pellets &/or flake with the beloved beefheart mix. I also made a seafood mix (fresh clams, mussels, shrimp etc) for them & mixed in their favs. Early on I "trained" the discus to eat from my hand & they'd at least try anything I held, anything at all, plain shelled peas included. Daily small water changes to remove poo & uneaten food helped a ton when I didn't do a major WC, but that was rare...