Signs of Fighting

I have 3 axolotls of 23cm, 18cm, and 15cm long, all in a 200L tank with large hides for each of them. I've never seen any signs of aggression between them but today I noticed that the largest has had one of her gills chopped/bitten off. The second largest has a small nick on his tail ridge and has had part of his jaw cut/bitten. The right side of his jaw is hanging a little and there is a small nick in the left side. He often sits there 'yawning' repeatedly. They still seem fine sitting right next to each other and the smallest one is fine.
Is there anything that could have caused this other than fighting? What is the best treatment? If I see the situation change or any signs of aggression then I will immediately set up dividers.
Since moving into this tank 2 weeks ago, the axolotls have been extremely shy, Rarely straying from the hides unless the room is pitch black. The largest has also not been accepting food much. She hasn't eaten in at least 3 days and whenever I put a worm near her face, she walks away.
Pictures coming..

A water test gave a surprising result: Ammonia 0.5, Nitrite 0.25, Nitrate 30
Very odd that the cycle still seems to be present, but is not fully controlling the waste.. Or do these numbers indicate something else?
I immediately did a 60% water change.


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The test indicates you're going through a minicycle. It should stabilize quickly.

Your axolotls look healthy and might just be injuring themselves by accident. If you don't see them fighting or bite marks then i don't think its aggression. Are you feeding regularly?