Where on the fish is the fungus, how much is there and what kind of fish... and a pic would really help.
Usually SW fish don't get fungus unless they have a bacterial problem first. Fungus is almost always a secondary infection.
Don't have a pic. It's white growth on the fins. I have them in a quarantine tank. Been using Melafix for a few days but doesn't seem to be doing anything. They are eating well though.