What kind of treatment did you use for the water before adding them in? Also, what's the temperature of the tank and what was the temperature of the water that the tetra's were in?
Without much else, it sounds like your fish are having a tough time acclimating to your tank. This could be caused by a number of reasons, but we'd need more information from you about your tank specs and how you acclimated them.
The most common culprits I've seen from poor acclimatization are:
- ammonica/chlorine (if your aquarium water wasn't properly dechlorinated/cycled)
- temperature shock (if there is a wide temperature difference between your tank water and the water your fish were in; anything >1 degree can be considered large)
- pH shock (if the fish are being moved from a basic to acidic pH environment)