Nandopsis haitiensus come from Hispaniola where "no" other species of endemic cichlids are present, consequently they don't play well with others. If you put it in a tank with other cichlids (other than a chosen mate) it will usually try to kill them, if it can't kill them, it will probably die of stress induced diseases.
Haitiensus prefer very warm water, mid, to high 80s, and grow very large, so a tank of 150 gallons would be what I consider minimum.
My male easily hit 15", the female about 10" in a very short period of time, and the pair did well for years in a 150 gal tank, with no other fish, and raised tons of fry in it.
They need very clean water to keep from becoming diseased, my water change routine was usually 30% every other day, with vacuuming of any detritus (although they tended to attack the vac and my hand with impunity, often drawing blood.)