The problem I find with most standard info about cichlids (especially Central Americans), is that most info seriously under states the space needed to keep them.
I have snorkeled with JD's and others in nature and often find 7" Rocio's (JD's) will guard a territory of at least 250 gallons square against all other cichlids, and in the standard literature a tank of 75 gallons is considered OK. To me this advice is BS, and its no wonder aquarists that follow the advice end up with aggression trashed tanks, and dead fish. And those that rehash that advice, to me, are giving others bad advice
And often old literature will state certain cichlids are loners, when in a large enough area many live in loose shoals, and do well in that social situation, and need it to stay healthy, long term.
Of course, they will not display this natural tendency in a tank the size of a rut in the road, which is the size of a 100 gallon tank in many cases.
And in the old literature a limited number of water changes per month are thought to be adequate, when in nature these riverine cichlids live in constant water changes for certain parts of the year.
Garbage in, garbage out.