oscaroo - while I applaud your enthusiasm, and the fact that you are doing research before you buy your next fish, as it now stands you don't have an aqequate sized tank for your current oscar. Right? So ideally the new tank should be for your oscar, and your then 'old' tank would be better suited for fish that won't get so big. Allan's suggestion about an Acara might be just the fish that would fit your 60 gallon tank. A 36x18 footprint really doesn't allow any type of monster aggressive fish. My advice, start small, get some experience under your belt, then start looking at larger tanks, and larger species of fish. Over time you'll have a lot more fun, and spend less time dealing with sick fish, such as your first oscar that came down with HITH. There's no rush, plenty of time for bigger tanks & monster fish.