What happened when you added fenbendazole to the water? Someone on the site has offered to sell me some, and I was going to buy it. Is there a problem with it? I think you can by flubendazole as an aquarium product that is a fish dewormer, for what its worth. A friend of mine that keeps Discus told be about it. He said fenbendazole should be sprinked on the food and ingested, and flubendazole can be added to the water, but he didn't know what would happen if you added fenbendazole to the water.