Imo people are just seeing the normal life cycle of ick and think the poly is working. I don't doubt it probably helps manage it and therefor reduces the numbers of spots one might see. But I think it's far from a cure. If the makers of this product could show non biased test results and how they obtained success then I would look at it more closely, but I'm willing to bet they don't have the data to back up there claim.
Perhaps it was a coincidence... but before the treatment the tang was only getting more and more visible spots. Perhaps the tang built an immunity, but that doesn't explain why he didn't fight it off the first time, or got it just as bad the second time around. Maybe the tang built up immunity exactly when I started adding the medic. Or maybe the medic worked.
Sure, this isn't exactly a scientific research study... but I'm happy with the results I've seen.