They are effective vs. different parasites. I prefer Flubendazole to Fendendazole.
If you are in the states you can get both as well as levamisole HCL here:
http://www.inkmkr.com/Fish/ItemsForSale.html
Fenbendazole. I do have Fenbendazole 10%. It works for a number of things but it is not absorbed through their skin or gills. It must be eaten to be effective.
Flubendazole is active through adsorption into the fish’s skin and gills. The drug does not have to be eaten to be effective.
From the site above selling these drugs.
Here is the thing. A lot of the worms and parasites we may have to treat are not seen by us. So we may not easily be able tp diagnose the specific organism we need to treat. Selecting the medication to kill a specific knowm worm and/or parasite depends on an accurate ID of the enemy to be attacked. Knowing which med to use for which attacker is of little help if you have not accurately identified the specif worm and/or parasite you need to fight.
I normally keep these in my medical box: Flubendazole. Levamisole HLC. Metronidazole and Praziquantel. I may buy other meds for specific situations but do not keep them on hand. However, I do maintain and average of 20 tanks and find a med kit to be a big help.