This is my first saltwater tank that I purchased second hand with all the equipment & 4 fish. Its a 90 gal tank with a clown, blue tang, saltwater angle & I'm not sure what the other one is. I have this set up at my place of employment so I don't see it on the weekends. When I left of Friday everything was normal. Monday morning I came in to find my blue tang with a ugly red place on his tail. I have read every forum I can find & its all so confusing & I still can't decided if its infection or injury. Can someone please help. He seems to be eating fine & acting normal. The white spots were on him when I got the tank. She said he had had issues when he was younger & they were scars.