"50% water changes do carry some risks, and some advocate 80% post-levamisole water changes. "
I would agree with this. I guess it depends on what you define 'large' as...
"Might be really good idea to find the truth one day."
good luck with that, and let me know when you do
"Light-sensitivity: yes, I've seen this. It is not entirely certain if this applies to high-concentrated stored solutions only, or also to much weaker concentration in a tank, but if it does apply, it would seem that the huge water changes are just not needed."
Maybe I'm just old school, but if I'm putting something in my tank to treat fish it is not part of their usual environment. Once the treatment is over, I want them back in their 'comfort zone'. For me, this means making sure the temporary additive is completely gone. And I don't do 'huge' water changes unless there is some kind of huge emergency. . .
A couple of times a year I may add carbon to a filter I'm cleaning and then remove it the next time. Primarily, I don't use it, but if there is any lack of clarity in the water I will add it for a bit. Usually clears things up very nicely. And yes, I see no harm in adding it after medication. Sometimes it is essential. Even after levamisole, which will break down on it's own, I will add it.
Fishkeepers are a bit like fishermen. We all have our tried and true habits that we stick with. And it has been said rather frequently on this forum that, 'your mileage may vary.'
