I guess I think the BGK is a community fish as long as you have the proper conditions for it. I have read that a 10 foot tank is preferred, though that is normally out of the question, along with lots of dark hiding places a low lighting.
I feel like the fish wouldn't be very predatory, unless you have tiny fish like neons, in which I would say 80% of fish will feast on.
Yes. I have to keep in mind that we have many beginning aquarists on this forum, and they may take what they read and run with it. This is why when i spot something like here, I comment. I obviously mean no offense to anyone, but just want the facts out there.
On the BGK, yes, many will say 10 feet. Biologists generally agree that 6 by 2 is absolute minimum. Larger is obviously always better.
They have a small group (6-7) of this fish in a tank at the Vancouver Aquarium. I wish I had a video camera, because the last time I visited, a couple weeks ago, it was relatively quiet (visitor-wise) and I spent several minutes standing in front of this tank, which is a floor to ceiling (about 8 feet) by several feet front to back display, with a replica rock backdrop that has niches and aq couple large tree branches. The light is very dim, naturally, so at first glance you cannot see the knifefish, but once you spend some time, their rippling forms become clear. And it is remarkable; they truly are "ghosts." This is the habitat this species deserves. I thought at the time that if only I had a video camera I could have filmed the sight and posted it.
And, they are combined with a shoal of angelfish, Pterophyllum altum in this case. And they too are remarkable. They are about 4-5 inches now, and I think there are about a dozen of them. But again, the space is the point. They have formed their hierarchy, and they challenge one another accordingly. But no one is ever damaged, there is no physical contact, simply because they have the space to be themselves. They ignore the knifefish, and the knifefish ignore the angels. And in this tank there is a largish group of characins, Lemon Tetra I think they are. They are completely ignored by the others, and again it is all due to space. As in nature, where these fish do live together, they never get in each other's way.
You cannot do this in a 3 or 4-foot tank, as many wrongly attempt. It just won't work. The stress these poor and beautiful fish will be under will mean a shortened lifespan, and an unhealthy one.
Again, this is just an observation that seems apropos in this discussion.
Byron.