Had one in a 77g tank all by itself for about 3 years. Went from about 6" and pencil thickness to easily 1/2 the length of the tank and THICK. Beautiful eels, and even at that size it wasnt aggressive, although it ate all the hermits and emerald crabs I put in the tank, and knocked snails off the rocks and glass to their doom.
Oh and make sure to feed a varied diet and soak in vitamins, if not they will turn grey/white as they get into adulthood and arnt NEARLY as attractive. I fed mine about 10 different seafoods, always soaked in vitamins and it kept its golden color for many years.
Jon