If the aim is to house this fish at maturity (i.e., its lifespan), you will need a tank that is 6 feet in length, and at least 2 feet width, absolute minimum. Depth is not important. As Ch4rlie said, the inflexible body requires this.
As for tankmates, remember this fish is predatory and anything under six inches may be eaten when the BGK is mature. Well suited with angelfish, discus or the medium peaceful South American cichlids such as Geophagus species. Avoid any nippy or aggressive fish. Knifefish produce an electrical field used to hunt prey, and must never be kept with other electric fish. The fish listed in post #3 are not suitable tankmates, if that is intended. Aside from behavioural issues, there is a vast divergence in water parameters, especially GH; mollies must have moderately hard or harder water, but the BGK is a very soft water species.
As for feeding, since bloodworms should only be fed once a week, I would look to other foods quickly. Naturally a micropredator, eating insect larvae, zooplankton and small fishes; it will sift through the sand substrate when hunting food. In In the aquarium, they will appreciate frozen or live bloodworms, small feeder fish, tubifex worms, brine shrimp, ghost shrimp, etc. Can usually be weaned onto prepared foods. Small earthworms are relished and particularly good for getting new fish settled and eating. Nocturnal feeders, they should be fed at night. Once settled, they will often feed during the day, even from the aquarist's hand. [As is obvious here, a sand substrate is important.]
From the photos, you have another problem, and that is the lack of suitable hiding places, plus the need for dim light. Bits of bogwood with crevices and tunnels would be ideal; some use PVC pipe, not clear though. Floating plants are good to help dim the light.
A very specialized fish, and one that sadly does not live long often because it is forced into more basic "community" tanks where it will not usually do well.
Byron.
