The typical red/brown aceola flatworms are not all that bad. If you have lots oif excess nutrients in your tank they can get out of hand and removing them is the dangerous thing when they get bad.
if you just have a few that you can see i do recommend using Saliferts
Flatworm Exit according to directions as it is relatively easy and safe to use if you dont have mass amounts of them. The danger in treating for them isnt the actual chemical used, but toxins released into your water when mass amounts of them die at once. If you only have a few you can nip them in the bud without much concern for damage to any of your tank inhabitants.
http://home2.pacific.net.ph/%7Esweet...itchworms.html
at the bottom of that page are some pictures of the more common acoel flatwrms which is more than likely what you have if they are indeed flatworms
