Clownfish tail damage: aggression vs disease?

[fishwater]

I noticed today that one of my clowns has a chunk missing from its tail fin and when looking closer, maybe its dorsal fin too. The tanks around three years old. I have two clownfish that have been together for at least a year. They always seem to get along. The one with damage is the larger of the two. I also have a hippo tang and a white spot puffer. The only aggression I've seen in the tank is the hippo will occasionally chase the puffer when I'm feeding.

I haven't added anything new in at least 5 months. I don't have any water testing supplies left, so don't know parameters (first stop tomorrow is getting new kit).

Does this look like aggression or fin rot?

Thanks