Flukes. Make a Freshwater dip by buffering some RO/DI water to match the pH of your tank (you can accomplish this by using baking soda, alkalinity buffer, or something like pH 8.2 by API). The temperature needs to be consistent with that of your tank as well. You can choose to add additional medication to facilitate the removal of the flukes--as aforementioned hydroplex works great as does praziquantel (also known as Prazi-Pro by Hikari). Dip the affected fish for 1-3 minutes while monitoring them to ensure the fish doesn't stress out too much, if the fish starts thrashing or otherwise acting erratic remoeve it immediately and try again in a few days.. Most fish can be dipped easily and wont have any problems. Flukes are very easy to get rid of if you catch it before they infest the fish. You may need to dip the same fish multiple times (with a few days resting time between dips) in order to get rid of all the flukes..