Never much cared for the tang police. Get some experience, read as much as you can, and get the best quality foods you can, and I think you'll be doing right by your fish. Giving them a great environment to live in is crucial, as well; I didn't intend to let that aspect go unmentioned.

Someone mentioned cats. Keep one cat, and then let it out. Does it stay on your porch? In your yard? No, it utilizes all the space it can. Does that mean it is cruel to keep a cat in a 400sq ft apartment? No, I don't think so. Animals adapt to their environment. Still, you do have to monitor their size, and make adjustments as needed.

They have no need to run from predators, nor do they need acres of reef to forage for algae growth. As far as swimming room, I can't really say that they don't like turning around after X amount of feet. I keep a tv next to my aquarium and put it on NASCAR races so they will learn to turn left. Watkin's Glen really screws them up, though.