Geophagus are generally the least aggressive SA, but not my experience with Geo iporangensis, a dwarf cousin of brasiliensis. Mine is picking fight with every tankmate of equal size and dominate over tough Cryptoheros species. I have two of them, but I have to separate them as they showed excessive con specific aggression until the weaker one lost an eye from fighting. The one eyed Jack has not lost its aggression, still picking fight with tankmates.