I hope it works out for you and I hope you are able to keep him. They are amazingly beautiful fish. I am also surprised that he runs a 500G with all those other fish in the tank. He must have some huge personality.
The 8" male I have (also from freshwaterpredators) is currently paired with an 8" female in a 350 with an 10.5" Gold Saum and the pair does not mess with my Gold Saum at all. Infact the Suam owns that tank. Just goes to show you the personality is still up to the individual fish.