What is this and how do I treat it?

[Paxy]

Just noticed this on one of my tetras today. Any idea what it is and how I’d treat it?

 

[Boundava]

Looks like an ulcer,. usually from poor water quality. What are your water parameters?

 

[Paxy]

I change out 15 gallons weekly in a 36 gallon tank. Here are the current water parameters

 

[GaryE21 136]

It looks like Mycobacteriosis. If it is, it is untreatable, fatal and it spreads if left until the fish dies.

 

[Paxy]

It looks like Mycobacteriosis. If it is, it is untreatable, fatal and it spreads if left until the fish dies.

Thanks!