What is wrong with my fish? (middle left)

It’s hard to see it in that picture. It looks like the tail has fungus attached, maybe some more around the body. Not letal if you treat it soon. Someone suggested you to put the fish alone in a hospital tank. If fungus, it’s easy to treat. Sometimes it’s just an opportunistic disease that takes advantage of a weak immune system. I have only seen it in fish with injuries or newborn babies with deformities. Hikari is the best brand for fish meds. With fungus their treatment acts fast, in one day you can see the difference. Don’t use those “natural remedies” pimafix melafix etc… they’re just snake oil. Wish we could see a picture with more detail.

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