yes, definately. I would also not feed flake foods as a source of their main food. Especially the clown and angel, they'll lose color if not provided with a varied diet. A cube is frozen food. There are some frozen foods that are prepared in "cubes", for easy preparation. I always suggest Marine cuisine. They should sell it at your LFS. It's a frozen concauction of brine, mysis, and krill, with a "color-enhancing additive". My fish go crazy for it. I also put in a sheet of nori (dried seaweed) about once or twice a week. They go crazy for it as well. The angel is a grazer, so having that in there for her will help a lot.
Snail makes his own food out of a bunch of different things, throws in in a food processor, and then freezes it in small cubes... it's a great idea, but i don't have a food processor. He uses things like squid, clam, shrimp, and some other stuff too. You can ask him about it.