Is this a true Elephant nose knife-fish (Sternarchorhynchus oxyrhynchus) or Peter's Elephant Nose (family Mormyridae)? People tend to miix up the names.
If this is a Peter's Elephant Nose, then I would say that this is a very finicky fish to keep.
They grow to be 20-30 cm in size so a 30G is minimum. These guys are also very very picky eaters. They emit electrical pulses that can make other fish uncomfortable.
Also they are scaleless and thus more susceptible to water conditions and medications.
In general, they're not considered great planted tank community fish (not in the sense that most members here on TPT stock their tanks).
Having said that, they're gorgeous and I do wish you luck.