The Polys and BGK seem fine together...sometimes the BGK will open it's mouth and try to chase off the Polys from it's space, but they usually ignore her, lol! Basically, no damage done between the 2 species. However, my Dats, Pike, and BGK tend to go at it here and there, but no serious damage done though. Usually the BGK is the aggressor, but they all want the same hiding space.