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As you may know, my little red eared slider has ear abcess. My sis boyfriend then told me that he used to have two turtles and one of his turtle has gotten ear abceS's and he saw the big turtle trying to bITE off the abcess. In the end, it successfully bit off BOTH sides of the turtle's ear abcesses and its wounds healed and it became normal. That's weird, because my turtles (big n small) has been living together for a long time and I've never seen the big one trying to attack the small one. Then, ever since my lil turtle has gotten some ear abcesses, I've seen my big turtle trying to bite its head off. I'm afraid, so I separated them. What should I do? My sis boyfriend wouldn't lie to me like that.

He may described what he saw, but that is incredibly dangerous for the turtles involved and whatever else in the tank. It's not unusual for turtles to attack each other, especially at an injured area. A turtle will have no defense at another biting its abscess. It's extremely lucky if it dead heal normally after that incident.

As for the aggression in your tank, it's not unusual as I mentioned before. But they can and usually do become aggressive, thats the problem with keeping more than one turtle.