HELP! Fish with unknown growth

[Browneh89]

Hello,

I had some fish passed down to me from an extended family member who passed away. I've been looking after them, feeding them and cleaning/testing the tank regularly however one of them has got a growth, looks like an infection or a ball of fungi.

I've put fish medication into the tank which came with them from the previous owner but it's not helped, does anyone know what course of action I need to take?

I have linked a video below of the fish, would genuinely welcome and appreciate any advice.

 

[MaloK]

I would euthanize that poor little thing asap. Before it contaminates the whole aquarium