Fin rot is progressive and makes the fin sort of 'dissolve' over time. Hence the name fin rot since it looks like the tail is slowly rotting away.
Tail-biting can happen overnight and unless it's an advanced case of fin rot, then only tail biting can cause chunks to be missing from the tail.
If a tail is being ripped, however, this can also appear to be fin rot. Things like getting caught on decorations or excessive flaring can cause very clean, yet frazzled looking rips.
If the rips don't heal over a few days and get bigger, then it is possible that it could have developed into fin rot~
hope this helps :D
Last edited by ZackyBear; 06-13-2012 at 01:26 PM.