What kind of danios and tetra? I think you are at a comfortable bioload right now. I wouldn't get a dwarf guorami. I had answered your other thread about male gouramis. You did not mention that there were fish already in the tank. I suggest that you stay where you are or buy a bigger tank. Even a 20 G would help a lot. The system in such a small tank is very unstable, because of the volume of water. Overstocking it would make it very hard to maintain. Easy maintanence, IMO really ups the enjoyment of this hobby. Hard maintenance turns new people away from this hobby.