White stuff on my fish's back

Hi all

So I was checking up on my fat Banjo again the other night, and noticed white patches on her back around her dorsal fin. So next day I did a 30% water change and kept my eye on her, and I see it's still there.

Could it be an injury? They don't have scales so I assume her skin would be more delicate, especially with their digging. (I have normal pfs as substrate)

My other thought is fungus? I have kanaplex that I can treat with, but I don't want to just treat the tank unnecessarily..



Parameters have been pretty stable since I first introduced her to this tank last year, only my NO3 has been a bit high recently but still under the "acceptable" range according the liquid test kit I used.