My Arowana of almost 2 years is experiencing some health issues. Recently I noticed a small hole forming in the center of one of the segments of his dorsal fin. As days passed it began expanding outward, vertically, in both directions. Now there are about 6 or 7 holes on his dorsal/bottom fin. His front fins(hands lol) are showing some black discoloration at the tips. He also seems to be swimming a bit slanted, as well as acting a bit jolty and nervous but apart from that he eats fine and swims around normally. I do not believe stray voltage is causing this issue because the other 5 fish in the tank are fine. Does anyone have an idea of what can solve this dorsal fin rot? I do not think it is lateral line erosion because he never has any holes or sores on his body, apart from when he smashes his head on the glass.