Wound on fish

Hi all


I’ve currently got a fish in my tank that is eating and seems happy but has had a small white zit like wound that started on the side of his belly but has seemed to move from one area of the body to another? This has been going on now for 4 months and is now getting worse by the day. I have tried many different medications and ideas from local pet stores as well as researching online, I’ve also tried removing him in a net and used hydrogen peroxide but to no avail. I currently have a tank full of Australian rainbows and none of the other fish show any symptoms and all seem healthy? I do 50% water changes weekly and have not had any other issues over the years. If anyone has any ideas it would be much appreciated. I’ll try and upload some pictures too

Thanks in advance

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