one thing i will say as of this morning, which is the final day of the dosage, is that this stuff will kill fish. Essentially, it is a poison to all living organisms in the tank.
That's a bad assumption.
By the time fish have clearly identifiable symptoms, they've got so many worms inside of them that they're already quite weak. And then quite suddenly, the worms die, and must ALL be successfully passed. This is a highly traumatic experience, and a lot can go wrong, resulting in fish death. They may either fail to detach and then rot, or clog up the intestines entirely. The callamanus treatment document linked earlier in this thread makes brief note of this:
"Dead worms inside the fish may cause future mortality."
But more documentation is available elsewhere.
I lost a few fish when I initially treated for widespread callamanus infestation in my tanks. But during the follow-up treatment to knock out any new worms from eggs, no losses. And also no losses during the many, many times I've used it subsequently, using it as part of my standard QT protocol.