I've got a 240 gal with 10 Piranhas, I have a 180 gal with a Silver Arrowanna and a Motoro Stingray. Then I've got a 90 gal with 6 various Discus:)

They take about an hour a week(in total) to take care of, and can be cheap too, if your lucky. I got all my fish and tanks for dirt cheap because my friend ran a pet store. And the filter system I use has washable inserts so there is no weekly charges or anything once it's set up.