Brown white eyed moray eel

[Dangerousdan]

At lfs they have above mentioned eel, its currently just under 2ft long and quite a chubby looking thing. When i asked the size this eel gets the bloke said about another foot, so if we said about 3-3 1/2ft would this be about right?
What size tank would this need to be kept in?
Anyone with any infomation much appreciated.
Thanks
Danny

EDIT: Being doing me research and am 90% sure ive found the eel i mean. This being Gymnothorax thyrsoideus