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.

Do you think blood worms and a few flakes would be ok then, because I have a box of flakes and don't wanna have to throw them away!!  I'll look into gettin some pellets tho.

Also, how often is best to feed them??

Sinking pellets are great for moors! While I had my first moor, Mr. Popo, in quarantine, I fed him only sinking food and he was eating really well from the bottom Later when I introduced one of my fantails to him, he learned to imitate her and find food by the surface

If it matters, I feed my fish three times a day (unless I'm at work, then it's only two) pellets in the morning (sometimes in the evening) and veggies or live foods for dinner