All the grammodes I've kept (about 8) have been consummate hiders, they'd only come out to strike at food, then quickly back to their hole.
Or when they are guarding fry, to protect them as the fry school. They are lurk and strike predators.
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male above female below
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The pair above killed any other fish I tried to house with it, cichlids, dithers like live bearers, it didn't matter.
I had a friend who kept a pair with other cichlids, but the tank was a 240 gal, and the grammodes owned about a third of it, allowing no trespassers