What is the reasoning for a 100% water change? Is there eggs or something in the water column? Seems like more stress for already stressed fish.
If it's for removal of the chemical, wouldn't a large water change and carbon be a better option?
From what I understand the Levamisole only kills the adult worm, not the free swimming larval stage so the 100% water changes are to remove those, but ya, 100% sounds really scary! I recently did a 50% when changing my substrate and my rummynose tetras went pale and wouldn't talk to me afterwards.