Anyhow, mine has hit the sad ending of its story. Haven't seen it all week so finally decided enough was enough and took apart the tank. He's not in there. Not in the sump either. Either he perished and was scavenged (found a nasty large red eyed crab while taking the rocks out) or he's managed to find his way out of the tank. Either way, no more eel.
This has been a rough stressful ride the last 4 months trying to keep this thing happy. I don't think I'll get another.