You may be right. I'm still going in multiple times a night to kill them. I found one of my frogs eating on this morning off the glass, so maybe they will be somewhat useful for reducing their numbers.@JasonE,
I've been where you are - driven half-mad by those f*cking flatworms. When I finally gave up trying to get rid of them (my rounds of Prazipro started hurting the plants) they disappeared by themselves in less than 2 years. I am suspicious that happens for most people since you don't hear many stories of people who have had infestations for years on end (though maybe the long-sufferers stay quiet?).
@Johanovich I have not seen these flatworms kill a large isopod, but the small tropical red and whites could be subdued and killed so isopods are not entirely immune to the flatworms.
My dwarf white population in that tank is great. If they are eating isopods it can't be in large numbers. They're clearly producing more than the flatworms are eating.