Since black moors are egg bodied shaped, I would recommend that you feed them a good quality sinking pellet.
Egg bodied fish tend to get very constipated easily, which can lead to swim bladder problems, with just a diet of flake foods.
You might also, want to vary their diet with frozen peas, with the skin taken off and slightly mushed, frozen foods, such as brine shrimp, bloodworms, and freeze dried shrimp. You might want to check around on this site there are other suggestions for feeding a varied diet. You will just have to try and see what they like the best.