Fin Rot or Nipping?

[JDigital]

I noticed a day or so ago that one of my angels had a "split" in its top fin, and roommate (knowledgable in FW) said its just someone in the tank nipping at it... however today I saw this on its tail fin (still split on the top fin, just not noticeable in the pic)



Does that look like fin rot? or is there someone in my tank that is nipping at it... I have seen the other angel chance this one, but never seen it nipping...