With almost every cichlid, choice of tank mates and whether the tank can be planted or not, depends on tank size.
If the tank is small (100 gallons or less/4ft length) your options are thin, any tank mates can be easily cornered, and in many cases rooted aquatic plants are torn up.
If the tank is medium size, 100+ to 300 gallons (6ft or more) your chance of aquatic plants and tank mates gets better.
Larger than 300 gallons just about anything is possible.
GTs come from an area west of the Andes, where there are few other endemic cichlids, so they tend to see other cichlids as competitors for food and territory, to be vanquished (probably where the moniker "Terror" came from..
I would guess shell dwellers will probably end up as expensive feeders as the GTs mature.
I keep Andinoacara coerleopunctatus (close cousins to GTs, in a well planted 180 gal and the plants are seldom disturbed.
For tank mates I use largish tetras, and a pleco, others that worked were Goby's. The Andinoacara seldom seem to notice the non-cichlids, unless small enough to eat.
Although I started with about a dozen Andinoacara, at maturity the Alpha male whittled the population down to 3 females, and himself, and the tank is now at a sort of non-aggression equilibrium.
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The above shot was taken when they were young (about half the size they are today)
One difference between GTs and mine, is GTs get considerably larger, so as adults, might need a larger territory for the tank to remain a DMZ.
Coerleopuntatus males (below) top off at only 7", GTs can hit 10-12".
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To gauge size of dither fish (in my case higher bodied tetras have survived 2 to 3 years in the tank)
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Early on, I tried some molly species that coexist with the Panamanian GTs in nature, and they were eaten. Maybe not fast enough, maybe they were too easily corned, not sure, and small minnow-like elongate fish were easily eaten.
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The Agonostomus above was almost 3", lasted less than a day.
Below one of the females.
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