You’re very welcome!
Yes, treating your dwarf seahorse tank with the fenbendazole (brand-name Panacur) at the recommended dosage – 1/16 teaspoon of the horse dewormer granules (22.2% fenbendazole) per 10 gallons of water – should eliminate the hydroids and will definitely destroy any and all bristleworms in your aquarium system. In fact, if you have a heavy bristleworm population, you should be prepared for a spike in the ammonia levels due to the sudden die off of all those prickly pests at the same time.
Also, beware that the gorgonia may be sensitive to the fenbendazole, so it would be best to remove them during the treatment regimen to assure that they won’t be harmed.
Best of luck getting your outbreak of hydroids and your bristleworm problem well under control, Waterdancer!
Pete Giwojna, Ocean Rider Tech Support