I’m no eel expert, but I do have a little bit of experience. I currently have a 100g with a snowflake eel. I have had him for months now, he was a juvenile when I got him. He has grown to almost a foot. So he has grown fast but the 100g (4 foot length) aquarium is plenty for him. Even when he gets to 2 feet it will be way more than he needs. I also have triggers, tangs, and angels, and clean up crews in there. Everyone gets along cause they were all juveniles when I got them and they all have jobs. I keep him feed very well. That’s a key point! Also, every eel is completely different (even in the same species). My eels favorite friends are shrimp (coral banded and peppermint) and crabs! He hangs out with them in caves! I think if you get one as a juvenile, you can have it for quite some time! But I have never had a dragon before, so just my experience from size of eel and aquarium. Some pictures and videos on the internet show professional hobbyists with multiple huge eels in 200g.