Hi.. I had a juvie rottk sev, Rambo, that was just beautiful but at about 3 1/2 inches he decided he liked to nip my angelfishes fins.. I tried redecorating, times out etc nothing worked.. he had to get rehomed.. If I had to choose between a sev and my discus there would be no choice.. Find him another tank with tankmates that don't have a lot of finage. Even if he doesn't hurt the discus the stress will cause them harm.. Good luck Sue