Golden Barb has red spots

I have a golden barb that has red spots on the side, or rather my friend asked me to fish sit for a month then decided he didn’t want it back. So unfortunately I have a fish that is too large for my current aquarium and not sure what to do. He has been fine for a month and a half but now has red spots on the sides. I’m barely even a hobbyist cause I only have 1 tank. I put the barb in a 5 gallon bucket with 1 floating plant, water from the tank, and a rock but I know he can’t survive there for long. I’ve added fungal and bacterial infection medicine to the bucket since that’s what my friend had given me just in case. But I’m thinking it may be more parasitic.

Unfortunately even if he gets better the tank is still gonna be too small and he will remain stressed. I do not have wife permission to upgrade the tank as she barely tolerates it as is. Any options besides a funeral?

(Put him in a tiny bowl for photo.)