I'm guessing flukes. There was occasional flashing before, which appears to have gone away now. And throughout a week of daily WCs, the fish didn't really change--lethargic, staying at the bottom, eating little--but as soon as the PraziPro was in the tank, they were moving about, doing their normal fighting, and eating well (even the one at the bottom of the totem pole). I'm sure the WCs helped at some level, though--they always do--and I'm already enjoying how much easier it is to clean with the very thin layer of substrate.