Bichir With Fin Problem

[ghostknife597]

I have two small bichirs, the normal cheap kind you'd find at a LFS. they are both about 4 inches. the end of the tail fin of one is yellowing and bent inward, and he doesnt seem to be able to move it much. the other bichir's tail fin appears to be fine. what is wrong with the first bichir's tail fin? any help appreciated

 

[Mr._Fishy]

Tank size, water stats, and other tank mates? how long has the tank been set up for?