David: Is this one discus or a group? Is it an adult?
Whenever I run into this I start with salt (non-iodized sea salt). Use 2 tablespoons per 10 gallons. Ususally you will start to see the other gill ease up within an hour or so. Adults can usually handle flukes. Its the youngsters that can have a very serious problem with them. If you are going to treat for flukes I would suggest that you try formaldyhyde (37%). I use 10 ml per 10 gallons. Then do a 50% water change after 8 hours. Make sure you have lots of air because the "hyde" sucks it out. You can usually find "hyde" at the drug store.
I have not tried trichlorafon b4 so I am not aware of it effects.
Jim