This is the section where speed matters, so it is worth spending two extra minutes on the first post. Most sick-fish threads stall because the answer depends on something nobody thought to mention. Give us all of this at once: What you can see — spots, film, frayed fins, redness, swelling, clamped fins. A photograph beats any description, even a blurry one. How it is behaving — gasping, hiding, flicking against objects, not eating, sitting on the bottom. Water parameters , as numbers. A great many "diseases" turn out to be ammonia. When it started , and whether anything new went into the tank in the fortnight before. What you have already tried , including any medication and its dose. This changes what is safe to suggest next. Please do not start medicating before you know what you are treating. Stacking treatments is a common way to lose a fish that would have recovered, and it makes the problem much harder for anyone to read afterwards. One house rule, and it is the only one that matters: answer the question that was asked, and say when you are not sure. A confident wrong answer costs somebody a fish.