looks like red planaria, they are easy to chemically get rid of.
Salifert Flat worm exit will wipe them out in a day or two. When dosed most die with in minutes.
Note they do give off a toxin when they die, if there is a crazy amount of them you should try to siphon as many out as possible. Also a bit of new carbon will help, also filter sock to scavenge them, you can also just take a fine net and scoop out the floating flatworms. I do not think you should try to live with them, they can get all over the place.