I would isolate him in his own tank during treatment so not to get your other stock sick & to use less medication. I've used metro, product call Clear & even mixed garlic in with its food then force feed FHs in the past hoping to rid of the internal parasites. I've only resorted to force feeding them after about 3 weeks without food. It's just that the longer they go without eating, the weaker they become & their immune system entirely breaks down.
Having tried these remedies, I think the best treatment is to keep the water quality at its best & salt with frequent water changes (daily). Good luck to you.