I'm generally loathe to get on a soap-box and share my frustrations but I'm going to here. In the interest of honesty and candor, let me say that there are many amateur fish keepers out there who keep cichlids....but shouldn't. Over the years, I've learned, and continue to learn, a lot about these fish, the industry, the hobby, etc. Of the many things I've learned, one disturbing fact is that there are too many amateur aquarists who behave badly with respect to keeping these wonderful fish.
I've seen way too many tanks that contain multiple species of cichlids which are grossly incompatible or, worse, grow way too large for the tank they're in. Often times the former is on purpose. Sure, any hobby can involve people that disrespect it. There are fish keepers who think it's cool to have a contest where they plop a bunch of incompatible cichlids into a tank just to see which is the nastiest. That's not what the hobby is about, and managing your tank this way disrespects these living creatures, not to mention the hobby itself. Please don't keep these fish if your intent is to watch one fish destroy another.
If you're keeping a handful of Oscars in a 55 gallon, please understand that you're depriving a beautiful cichlid species of a legitimate life. Sure, Oscars are cute when they're juvenile size. So are juvenile elephants, cows, horses, etc. You wouldn't confine any of them to a 10' x 10' shed, so why confine a fish (or several) that can reach a foot or more in length to a tank that's only 4' x 1'? I'm not picking on Oscars because there are many other cichlid species to which this applies. Oscars are just highly popular. Serious aquarists place considerable value on the lives of their fish. Purposely keeping big fish in small tanks disqualifies you from being a serious aquarist.
The Cichlid Room Companion
Tropical Fish Hobbyist
American Cichlid Assoc.
African Cichlid Hub