It's amazing that the BGK and the elephant nose can live together! My friend's e-nose get ripped in half when put in with a larger BGK. Over the year, My BGK had "accidentally" killed several large and small catfishes that had wandered to its cave. However, if the smaller fish survive after the first few days with the BGK, things seem to be ok. Probably yours is also the case, where the two of them are so used to each other's electric field that they learn to live in "harmony".