Levamisole can be added to the diet at 0.1% of the amount and fed for 7 days for removal of nematodes.
Tramisol Levamisol for Worms in Koi
Levamisole (Tramisol) – by Doc Johnson
As a water additive, Levamisole Phosphate can be used effectively as a dewormer for Goldfish and Koi, among other species, as an indefinite and safe treatment. The dosage is 0.5 ppm (zero- point-five PPM) added directly to the system without impediment to the filter or fish.
Levamisole / Tramisol will NOT KILL FLUKES
“Almost any veterinarian can and will get Tramisol if you ask nicely.” ~ Doc Johnson