Oooh. Karazy brings up a good point. If you plan on keeping the tank open top you should rethink the eel I'm afraid.
Trust me - I know how awesome they are and how tempting it is. But it is literally only a matter of time before it will crawl over the edge or jump straight out.
The first golden dwarf I ever had, escaped a tank that I thought was locked down like Fort Knox. You would be amazed what they can get out of. And they will try, sooner or later, they are just naturally curious that way.
What you can do, if you're really set on keeping him, is build a canopy of sorts. You can still keep it open top if the edges all around are fenced off, but it will need to be a minimum of 8" tall. I have seen them jump out of a bucket and clear easily 8" out of the water.
Sorry. I know it's not what you want to hear but trust me there is nothing more heartbreaking than finding your beloved golden dwarf eel as a fossilized stick on the floor.
