Honey gouramis are very docile fish, and I can't recommend that you mix them with blue gouramis. I'd be very concerned that the blues would harass the honeys to death. Also, I just finished giving my male/female pearl gouramis back to my lfs. They were outgrowing my 29-gallon tank, and its only other occupants were one honey gourami and seven bottom dwellers. Thus, I can't recommend that you keep more than one pearl gourami in a 20-gallon hex. In fact, I can't recommend that you keep even one pearl because they need more room to swim across the tank. In addition, pearls are also very docile fish and I wouldn't ever mix them with blue gouramis due to the blues' reputation for aggression.