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I'm kind of an optimist when it comes to things like this so I'd want to say it would be fine. I've never kept them but you would think since you keep convicts and firemouths or other cichlids of that size in a 55, a 20 would be ok for smaller fish like that. I'm not an expert by far so I'd say try and find a couple profiles of the keyhole online and see what the common theme is.