Need help identifying this

[asylumdown]

Depending on what it eats or how quickly it multiplies, it might become a problem. When my tank was first set up I developed an overwhelming plague of the little red/rust ones. They didn't seem to bother anything, but man were they horrible to look at. They were so think on some rocks I actually thought they were coralline algae.

Look closely at your tank and see how many of them there are, and then monitor them closely for numbers. The ones that aren't directly harmful can still crash a tank if enough of them die all at once, as some of them release toxins when they die. I'm pretty sure flatworm exit works against all flatworms if it gets to a point where they're a real problem, just be sure to follow the directions.