Well its a cool peaceful fish, not a lot of color but very well behaved. I keep it with severums, rainbow fish, plecos and a Pike which may or may not make the final stock list of this particular tank.
It is not a xinguensis- then it would have orange and a wider body- could be one of many "port cichlids" - lets see if we can get someone to proper id
duanes
It is definitely not portalegrensis.I have kept many of these over the years and it is nothing like the op's fish.
Portalegrensis of that size would be much more rotund, have more pronounced scales and the fins would be different.
I have no doubt it is krobia guianensis.