The Jar may be the issue in the long-term. ime Fire eels are out and about fish, and also abit neurotic in their behavior. Mine will dash and dive around the tank like holy terrors when feeling frisky. This may spook your jar or initiate an attack on the eel. Jars are notorious for "turning" on tank-mates. So it's something to really watch-out for. As for the eel 'n CLs I agree there shouldn't be a problem unless the fire when larger decides to try and eat one. their growth rates are very different. plenty of hideing spots for the eel and Cls from the Jar may be all the prevention you'de need.