Flatworms

Hello All. Over the past month or so, I've notice very small (about 1/8") spots all over my rockwork and bare bottom tank. They're mainly in low flow areas. The spots are reddish brown or rust colored. I picked up a small piece of live rock and noticed they crawl very slow and also noticed one on my glass this morning. The are not on any of my corals including SPS and LPS - they don't seem to bother anything.

Should I worry about them or treat the tank? I don't want to use a treatment such as Flat Worm Exit if I don't have to. If they're harmless, I won't treat the tank.

Thanks in advance for your help.