I agree with CWC on the goldfish. Most that are kept in constantly warm water will lose the color of their scales over time. This is not a sign of a healthy fish. It's also something that's permanent. A goldfish of mine was once kept in a tropical tank, and it became a pinkish color (really beautiful, but not his natural coloring). He has been in a temperate tank for the past year, and has not regained any of his color.
But...
That's not what you asked about.
I have made my own food from spinach, bloodworms, shrimp, zucchini,
spirulina, and gelatin (to bind everything together), blended in a Magic Bullet, then frozen. Slice off little bits a bit before feeding time (to let the stuff thaw), and drop in the tank when it's ready.
Nori is a good supplement. Very high in some vitamins and minerals.
I'll feed my fish nearly any veggie I have around, and this is in addition to Omega One
betta Flakes,
herbivore Flakes, Sinking Goldfish Pellets, Hikari Koi Pellets a leftover bottle of Tetra Color Enhancing Food, bloodworms, shrimp pellets, algae wafers, and freeze-dried daphnia. The betta gets mostly Betta Flakes, with the others as supplements to his diet. The goldfish and koi get mostly Goldfish and Koi Pellets, with other stuff as supplements. The Community gets a pretty even mix of all of the food. And the murdering molly gets mostly Herbivore Flakes with other stuff as supplements.