I bought the GT a week ago like this with a wound on his left fin. The iphone pics are not too good sorry. It looks like white milky substance is on the wound where the fin is split.

I noticed my Oscar on his left fin has a bit of the same thing today. He has what looks like a small tear. My water readings are Amm 0 Nitri 0 Nitrate 5ppm. Everything appears good and they are eating well.

I had the GT for about a week now, he is smaller than the Oscar. The Oscar was not happy he came into the tank. The GT made camp on the left side of the 75 gallon tank. He is 2.5 inches and the Oscar is 3.5 or so. When I shut off the light I can see some fighting going on. The agression is coming from Achilles my Oscar fish. He also has been in the tank since the start. I will keep an eye on it but it appears to be from fighting. The GT is getting bullied but I have observed him to be flaring out and fighting back, in the beginning he would just swim away.

Petsmart multiple times assured me it was from this GT fighting with the other GT's in the very small tank they had them in. The other GT's were banged up bad! I don't understand why they put them in such small tanks all together like that.

I said it looks like fin rot and he said like three times it is not. He also was hesitant to sell me the fish because of my Oscar. He explained the agression of the GT and all. It appeared he was not just selling me the fish to "just sell it". So it made me feel better that maybe he had observed this fighting going on in the store and "knew" it was not fin rot

still hard to tell from the pics, but it doesn't look too bad.
And no fin rot,IMO. Just some nipping done to him.
Just take care your O doesn't do any more damage to your lovely fish.
Very beautifull specimen.
Like i said in te other thread, if your waterquality stays like it is now, he'll heal in no time.

Thank you, yeah I will take care of these guys for sure. Don't worry about that!

Doesnt look like fin rot to me. Looks like its the result of the oscar bullying it. It will soon heal up as long as the bullying stops