Geophagines are known for their aggression towards their own species and other conspecific species

You can have them in a tank full of fish and they won't bother any of them, but add another Geo and its all-out war

Don't worry, they're pretty dang hardy fish. My pair of G. surinamensis kick the snot out of each other all the time and I've never seen anything more than a mild scrape or a small tear in a fin. My Oscars get worse scrapes just swimming around their tank

What size are they, Tim? These guys do take a while to get to sexual maturity, but they will pair up and court quite a while before they're ready to breed.