Bump on axolotl’s head? Please help!

[VariaK]

I have two axolotls in the tank (105 L). Water temperature is 18 degrees. Water parameters are: NO3 25, GH 8d, KH 10d, pH 8.0, Cl2 0. I also use small sand. I feed my axolotls with shrimps and tropical axolotl sticks. Axolotl that is on a picture is smaller and less active, than the other one, he also usually eats less , but he always was like this. Today I noticed this white-pinkish bump on top of his head. I’m really worried, I don’t think they could fight, they are not aggressive.. What did I do wrong? Does he feel bad due to this bump?

 

[VariaK]

I have two axolotls in the tank (105 L). Water temperature is 18 degrees. Water parameters are: NO3 25, GH 8d, KH 10d, pH 8.0, Cl2 0. I also use small sand. I feed my axolotls with shrimps and tropical axolotl sticks. Axolotl that is on a picture is smaller and less active, than the other one, he also usually eats less , but he always was like this. Today I noticed this white-pinkish bump on top of his head. I’m really worried, I don’t think they could fight, they are not aggressive.. What did I do wrong? Does he feel bad due to this bump? View attachment 86355

 

[Calgarycoppers]

Please invest in an API freshwater master test kit the strips are highly inaccurate

that bump looks like an infection / abscess. I'd find a vet