The rummy-nose tetra is an excellent fish for the community tank once it is adjusted to its surroundings, but this initial adaptive phase can be a bit longer than for some fish. In the meantime, it tends to be sensitive to water quality, so test this frequently. It does not take well to addition of salt and many chemical additives, and pH fluctuations can kill it. It must be kept with at least 3 members of its own species, or else it will sulk in the corner and show signs of stress. Healthy species will adapt eventually to a well-planted tank and school actively in and out of every corner of the aquarium, their noses glowing brightly. In fact, they are some of the most ideal "schoolers", and really enjoy the company of their own kind. They will also be completely peaceful towards other fish.
-http://www.fishpalace.org/H_rhodostomus.html