I have a 20 gallon hexagonal tank (about 19" across and 18" deep) in
which I have ember tetras, pygmy corys and oto cats. All these fish
reach about 1" in size. I was wondering if it would be OK to add a
dwarf South American cichlid. One of the LFS around here has some
Apistogramma nijsenni and they really look beautiful.

Is the tank big enough for one of them? I do not want a pair, in case
they get agressive when breeding.

Would a female be safer (less agressive) than a male?

Is there any risk of the Apisto bullying the corys?

I have never had any cichlids, so I do not know what to expect when it
comes to behaviour.

Blue Gourami