My 5 FH's have always been in big tanks, but teemee is right in that if you have a male larger than 1.5" he will bully others (my male is 2.5" thereabouts and he always pushes my Dispar school around). That said, I'm worried that you'll be setting up a battle between the RG in a tank that size; especially if your live rock is on the thin side. They are great fish and tough to boot. Enjoy if you decide to get one.