My tire track eel is in a tank that has a hang on filter on it. Well, I never really see him much only at night, so I figured he must have buried himself. However, one day I was changing filter cartridges and he was swimming around in there! I thought oh that must have been an accident. But then later that night I checkd again and he was in there again. He can get in and out, ive now seen him do both, but is this bad? because i dont really now wat to do about this.