They won't get any larger than 3 feet in a tank. They're one of the smaller eels. I believe the Gymnothorax tile('freshwater snowflake') is even a tad bit smaller, but not much. I have a 'Freshwater' Snowflake in my full marine setup. He's only a little over a foot long, but he's already 3/4" tall. I'm thinking he might not end up too long, because of how he's growing so rapidly in gerth. Then again, maybe he spent part of his life next to a nuclear sub and he's going to be 20 feet long! Maybe not.