Hi, they seem to be red planaria flatworm like the ones pictured below. I find for a quick easy removal is to siphon the tank water WHILE continuously blowing them off your rocks and corals with a turkey baster and sieve them out then return water back into tank. Usually excessive feedings cause a bloom of these in my nano. This way, you remove as many as you like and wont shock your corals since you’re reusing the old tank water. Small water changes after will eventually drop the nutrient level and should get rid of them. Hope this helps
Be careful killing a large population in ur tank. Could kill more than just the flatworms if you don’t siphon out as many as you can. Also there’s certain wrasses that way them