I used to have Oscars....very cool fish.I've had tanks in the past. I always start out keeping up with the cleaning and maintenance but eventually lose interest. Had one 80 gallon extra high with two big oscars and and a red tail catfish in it. The catfish got big enough that he was starting to pick on the oscars (and they were probably 8+ inches long) so I had to get rid of him. He was probably at least 15".
Also had African cichlids for awhile. Those are cool fish. Almost like having saltwater fish in fresh water with all their bright colors.