Do you actually have a pair (male and female) G. semifasciatus, I ask because I bought a pair and the male reverted to female (if you research on the web it seems to happen a lot). A friend then had a major failure in his system and needed to lodge his fish, I took his trio of G. bellus. My quarantine system was off line and I knew and trusted the fish and system so they were placed in the display, where they and the semifasciatus lived together for 3 years with no issues. The bellus male remained the only male in the tank. My tank is 550 US gallons.