I have found that eels need a place to hide, most importantly. The biggest reason that I have found for the extra space, is that they are healthier in a biological environment that can keep up to them. If you enjoy feeding your eel every day, you'll soon realize how much they deficate. They only need to eat around 3 times a week. If you don't mind plenty of water changes, the eel is great. Eels are my favorite, so I don't mind doing a 50% change when needed. Lately, I've only had to do it once a week.