Don't get an Oscar or an arowana. You don't have a very large tank, and these are very large fish. Not to be negative or "rain on your parade", but 10" absolute maximum length is the largest fish that should live in a 55 gallon. In my opinion- some will probably tell you even 10" would be too large; it is a matter of opinion. But, what is NOT a matter of opinion, is that any fish that grows as large as the tanks width (12") would be cruel to keep. Won't even be able to turn around without bumping into the front and back.
You also mention plants. If you want a planted aquarium, large fish (especially cichlids) are going to make it very difficult, digging up and shredding your plants.
Question- why are you buying a juwel rio 240? You could get a standard 55 gallon (or even a 90 gallon - which would be just large enough for an Oscar) for cheaper than the cost of the Rio.
You also mention plants. If you want a planted aquarium, large fish (especially cichlids) are going to make it very difficult, digging up and shredding your plants.
Question- why are you buying a juwel rio 240? You could get a standard 55 gallon (or even a 90 gallon - which would be just large enough for an Oscar) for cheaper than the cost of the Rio.
