My sick baby

[Klakasharkie]

Hello guys, I have two axolotls in the same tank (same size and gender) but lately one has been showing worrying signs. Her frills have fallen out a bit. Her behavior is the same as ever, no signs of stress. Today, I noticed a red lump by her mouth and the tip of one of her gill stalks is a strange color (Exposed bone?) I was wondering what it could possibly be before I call up a vet.
Lump is on the left under her mouth in the picture
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I appreciate the help!

 

[Skudo09]

Have you checked the water parameters? It may be worth placing her in a tub of cool, fresh dechlorinated water for now. This will allow you to monitor her closely. You will need to do 100% water changes in the tub daily. Firstly I would check the water parameters. If you already have, what were the readings?

 

[Klakasharkie]

Water parameters are normal, outside of a nitrate spike. It's 80ppm at the moment, so I'm working on getting it down.
Unsure if it's worth noting, but the other lotl is perfectly normal, gills are as full and fluffy as ever. As I've said, the 'sick' lotl is behaving normally outside of the mouth lump and thinning gills. I still don't know what that is at the tip of the bottom stalk. If it's serious I'll take her to a vet, but Id like to see if anyone here knows what could be wrong. My mom thinks it could've been that she doesn't like being with the other one, since I recently put them together, but theyre not hostile to each other and are well fed