I have a small school of each in a 35 gallon tank and never had any problems with them. And I think they are both very hardy, I've had them all for at least a year, and never once had any disease, (I take that back, I did have a molly get cotton fungus really badly and die, and the tetras never caught it). I do notice the black tetras seem to school a little better, but will nip at each other occasionally, but they never inflict any damage. I also have 2 male guppys in the tank and they have never been bothered by either type of fish. In my experience I would recommend either one!