Hmm well I don't believe they are red planaria, they don't look red at all and don't take the same shape as the ones I've seen on google images. I don't think they are a huge issue because I see none bothering my corals. Maybe a wrasse is in my future, as a natural way to limit the population, but even then, it's not a guarantee that it would eat them. For now I think my plan will just be to monitor the corals and siphon the flatworms out whenever I do water changes. If they start bothering my corals, then maybe I'll take more action.