A bigger tank is better but if you only have a 55 that will work. So, yes you can keep one GT in a 55 gallon tank but limited to how you decorate the tank, so no big rocks as your center piece or big pieces of drift wood. Your aquarium will need to be as open as possible. The most important is water quality. You must do weekly water changes and have a good filtration system. Most local pet store GT s max out a 9 inches.

