Just asking and not tryin to be rude, but are you new to the hobby. Did you age the water in the new tank, did you cycle the tank? A test kit is a necessity otherwise you have no chance of fighting off diseases and stress. If you don't know what your waters condition is you won't be able to know what is happening to your fish. You could have high ammonia comin out your ears and wouldn't know it. Polluted water can be crystal clear. If no one is pickin on him it's probably fin rot. I can only suggest getting the test kit quickly and trying to make sure you parameters are in the green. Once that's established they're are plenty of medications that cover multiple diseases. Just remember to remove your filter material and keep your tank well aerated during treatment. Don't bother feeding the fish either most fish won't eat while medicated and those that do will usually throw it up later which will only compile your problems. Good Luck I hope your fish recovers and does it quickly, and if you are new Welcome.
