Bristletooth rashes

[Chroma]

Hi, I've had a bristletooth for about a month now. At first I started to notice white spots but then they went away and was still eating and didn't think anything of it but now it's grown into something much worse. It's got rashes all over and lost its bottom left fin.
Please help

 

[SlugSnorter]

just on the fins, or is it the whole body? any other fish affected?