My 4" red flag-tail is growing extremely fast. I noticed that its tail has tears that run all the way to the base of the fin. Water conditions are perfect. Tank mates....black aro, 3 bichirs, spotted leaf fish. I have never seen any of the fish go after him. The tears don't look jagged like a bite. Its a very straight line. I'm worried about disease. Non of the other fish show signs of fin rot or disease. Any suggestions?