I have a fishless frag tank that's infested with flatworms. And I've used Flatworm Exit on this tank numerous times. It does knock them back, but it never completely eradicates them. The problem is that while Flatworm Exit does kill the worms, it doesn't kill the eggs they leave behind. Thus, a second generation. I've even tried treating again 5, 6 and 7 days later in hopes of getting them before they can lay more eggs. Never works. Maybe someone can chime in regarding the "incubation period" for flatworm eggs. :headwally: