I expect they are expensive.
With a pair, you can lose one partner before they breed.
With a trio, you can lose the male before they breed.
So that is a bit of a no win.
My read on Apistogramma is that each female claims a territory. The male also claims his turf, but each gender is aware of the other's territory. Females will drive other females off, a behaviour wrecked by glass walls stopping escape routes.
I don't know where the 'harem' idea developed from - probably old male fantasies getting tangled into observations. I found I could keep a group of borellii together as the books used to suggest, but that was the only species that seemed to read. After a few disasters, if I had a single tank, I bought a single pair.
They are fickle. Once when I was overcrowded, I had two males happily coexist. Both simultaneously fertilized the eggs of one female, just as peacefully as could be. They follow no rigid rules. But a pair, in spite of the odds of losing one, might be a better wager.
