My goodness!!!! 3 tangs and an angel were already in a 4 ft tank. You add the butterfly on top of that already overstocked tank. Ya know, I try real hard not to get stuck on that bandwagon about small tanks and oversized fish, I gotta say something about this setup.
Not one of those tangs belongs in a 4 ft tank alone. You've got 3. That copperband is scared to death.
What are your nitrate readings by the way?
"Life may not be the party we hoped for but while we are here we might as well dance!"