Quick Cure
There is a small bottle of a liquid called 'Quick Cure', and its relatively cheap. I think it's one drop per gallon of water...It works really well!!
However, if you have a carbon filter you need to remove it. Though the direction say to remove carbon for 24 hours, most people and my own experience is you can remove and replace the carbon in a few hours, not 24.
Also, do you have an aquarium salt in your tank? Aquarium salt can aid in the destruction of certain fungi and aid in reducing stress and increase slime coat. Generally it's 1 Tablespoon for every 5 gallons of water. Hopefully you'll see an improvement in 24-36 hours.
Good luck!