TBH I don't recall exactly where I learned it. But it seemed to be commonly used by a lot of people. I've read positive things about it on a couple of koi health forums as long as it's used carefully.
I realize it's a "shotgun" approach and don't think it would be the first thing I reached for if I discovered a parasite on one of my fish. I'd rather treat more accurately. However, I was under the impression that it's very useful as a clean up tool when prepping a pond for fish, as well as treatment of external bacteria infections and parasite problems....
I haven't used it yet for parasite control. As stated, I try and treat for the problem... ie: prazi/proform C/ topicals and such.
Would you care to expand on why you don't use it? Any chance to learn and I'm all ears.
Thank you for your interest!
Grant