Yup. Regular red planaria... flatworms.
I have found the flatworm exit to be very safe, but the planaria release toxins as they die. These toxins can really harm coral and fish. If you have a large tank, you can make your own mixture out of Levamisole, which is a livestock de-womer under the brand name of Prohibit. Like Juan said, suck out as many as you can - siphon the water through a fine net and then you can pour it back in and keep going. I would siphon every one that you see for a week or more, swish out your chaeto (or dip it) a few times and otherwise do all that you can to physically remove them. Have water on hand for a large water change. When you treat, the worms start to melt and get slimy - this could take 5-10 minutes, but sometimes faster. Turn off all of the pumps (keep return pump on) and the worms will get slimy and bind together in areas where you can continue to siphon them out after you treat. Do not put this water back in. Once you change a bunch of water after the siphoning, then run as much carbon as you can.
This first treatment is the worst. Do it a few more times a week apart. The next few times is no big deal since you will have gotten nearly all the worms the first time. I have found that some can slip through with just one treatment, so do it a few weeks in a row to totally eradicate them. In the future, a simple dip in CoralRx or Bayer does a good job when introducing new specimens.
I cannot see the video, sorry.