Fin rot or what?

[Kubuspuchat3k]

Hey, everyone.
Something is going on with the fins of my fish.
I don't know how to describe it, so i attached 2 pics. Please let me know your input on this matter.
What can i do to prevent this, Medication ??
I do a 30 percent PWC every week. feed the fish every other day or so.
I feed the arawona freeze dried krill, and the rest of the fish eat 3 cubes of frozen blood worms.
Water parameters seem to be good, the only this is the PH is low and i cant seem to get it up, i hate to use chemicals for this.

 

[Tim Wheatley]

To me it looks like they've been attacked by another fish.

 

[Meagan.Marie]

I agree it looks like his poor little fins have been nipped.

 

[Jason7894561230]

Fin rot normally has black on the end of the fishes fins