Beef heart is good for discus especially but this food has raised concerns as ppl began making their own mix. The problem with this is the heart is purchased from local butchers with the animal having been injected with steroids and growth hormones which can prove fatal to fish. It's also very important to ensure that the heart is cleaned THOROUGHLY ie no fat on it at all before being minced.
Good recipe for this:
Beefheart (from free range cattle)
Spinach (cooked and wilted)
Banana
Spiriulina Powder
Garlic
Mince heart, mix contents. Cube and freeze for later feeding.
I feed my discus a mix of this, bloodworm block or Mysis and then sprinkle in a little Tetra granules to let them bottom feed.
They grow very well, are healthy and eat directly from my hand. They are fed 3 times a day.
My juveniles grew from 3inches to 4 inches in 3 weeks.
Hope this helps
M