Hi, im new to fish and this forum. I have a 4ft by 2ft tank which is currently holding about 40 gallons. In the tank are 2 musk turtles, a mud turtle, 2 silver shark fish, a pictus catfish, a hoplo, 6 corys and shoals of red eye, neon and red minor tetras. It has always been a peaceful community tank, until yesterday I found a red eye tetra with what I believe to be mouth rot. It could only be described as a growth by his mouth, and there was another little one by his fin too. I quarantined him off, but he has now died and ive found another one with a growth. Ive now separated the fish and the turtles, and turned the temperature down to 75. PLEASE HELP as to what to do next! I am very worried for my fish and as I said, new to this! Also if anyone could tell me what could of caused this that'd be really helpful!