barbs most likly as they do have a small rep for nipping fins (it only takes one), but tiger barbs are the worst for it, they just nip fins alll day.
are the edges of the fins white? or do they look raged, if they do go to tropical fish emergencys and ask if its finrot, a pic would help me identify finrot (i know it now because i had BIG problems with it, i lost my betta to it)
and how big is the tank? angles need about 100l minimum but i say 150l min and they need a tall tank with other big tankmates, (angles will eat smaller fish)