Just an FYI, the Geos and GT are South American neutral pH an soft water species.
JDs and other Central American Cichlids are hard water, high pH water cichlids, and to me, as a biotope aquarist, don't belong in the same tank,
and
beyond that,
because the JD and the GT are so similar looking, (same body shape, same mouth shape, similar iridescent spangling) they are bound to see each other(not as friends) but as an instinctual competitor for similar resources .
Your JD is not being mean, it is doing what a normal cichlid does, when confronted with what it perceives as territorial competition.
JDs and other Central American Cichlids are hard water, high pH water cichlids, and to me, as a biotope aquarist, don't belong in the same tank,
and
beyond that,
because the JD and the GT are so similar looking, (same body shape, same mouth shape, similar iridescent spangling) they are bound to see each other(not as friends) but as an instinctual competitor for similar resources .
Your JD is not being mean, it is doing what a normal cichlid does, when confronted with what it perceives as territorial competition.