I used to have a school of 6 Red-Blue Columbian tetras and a school of 6 Australian rainbowfish. I'm now down to 1 rainbowfish and 3 tetras. I know this is far from ideal but right now I'm not in a position to get new fish and when I move I'm going to be setting up a 50 gallon and I'm not sure if these are the schools I'll want in there. How can I minimize their stress while their school size is diminished?