Sorry for a derail, but I'm finding this interesting - I used fenbendazole on my 55 tank that I had to break down. Not knowing any better, I used it (based on recommendations) for a possible planaria outbreak. Now I think they might not have been planaria. Anyhow, it was days later when my fish started dropping like flies from columnaris. I wonder if the fenbendazole could have weakened the fish's immune system? (They ate a great deal of it, and I treated with it for days)
Again, apologies for the derailment...