For intestinal nematode infections of ornamental fish, several anthelminthics (dewormers) are available. Two effective and commonly used dewormers are fenbendazole and levamisole. Fenbendazole can only be used as a feed additive at the rate of 1.14 grams per pound of food fed for three days, with a repeat treatment in two to three weeks. Levamisole can be used both in the feed and as a bath treatment. One effective oral dose is 1.8 grams of levamisole per pound of food fed once a week for three weeks. One effective bath treatment dose is 2 ppm (mg/liter) levamisole for 24 hours, with a repeat treatment in two to three weeks. However, be sure to consult with a fish health specialist before commencing any treatment and always follow their recommendations.
https://edis.ifas.ufl.edu/publication/FA091