I would not put an eel into a NC24. You should treat your NC24 as a 20 gallon tank, and stock it so (especially because that is how much room it has, after you eliminate the false wall's volume). You could put a golden dwarf moray in there, however, the cheapest I've seen one is $250. Other than that, there are no eels that will go into anything less than 30 gallons.
-Sorry, didn't read aresgod's response first. Good Luck!