Welcome to Reef2Reef, PhantomX1!
The overall shape of this guy does look like a "red planaria" flatworm (Like JaimeAdams, I'm not used to seeing them through a microscope - great job, that!), which is mostly harmless, but can grow to annoying population levels. I had a _ton_ of those guys - and still do, but only in my sump & refugia. I added several wrasses (fairy, flasher, and sixline) and a target mandarin dragonet, and haven't seen one in the display since.
~Bruce