Can you give more information?? Are there spots on the head, fins or body? Does it have tatty and blood stained fins? What else is in the tank with it? if its in a bad way you will have to sacrifice it as it may be a bacterial infection that will kill the rest of your fish. If you give more information someone can suggest what the problem is and how to treat it. When you add medication you will need to remove the carbon from your filter or it'll just take out the meds.