cories with ripped fins

[extremebunny]

I got 2 new cories yesterday and I noticed they had ripped dorsal fins. I did not see at the store because the guy said they were new and they were quite small. they don't seem like they have diseases, and they were being kept with peaceful fish (tetras I think) at the store. How could this have happened?

 

[ImACoolguy]

With a few fish I have brought home this has happened. Their fins got dreadful but with clean water they grew back. No other appearant symptoms just fin loss. I am not sure what caused it for me.