Satanoperca leucostictas (wild from Guyana) that I've kept before have always left alone smaller fish. I have kept them with rummynose, colombian tetras, neon tetras and buenos aires tetras.
You will find a number of people saying you shouldnt really mix geos unless in groups but i have a singular satanoperca lecousticta, a singular satanoperca jurupari, a singular altifrons and two red head tapajos in a 100g and they all get along fine, its a bit of trial and error dependant on species. I have tried on 4 seperate occasions to add red humps but find them to territorial with geos of similar size
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