Those are definately red planaria. Harmless for the most part.
If you decided to engage in chemical warfare, I'd suggest syphoning out as many as you can. You can also blast them with ome fw as they will melt immediately and not release toxins. Then, go chemical. Make sure you have filter socks ready to catch the sea of death, mucho carbon and some water ready for a big water change.
If you can remove your fish, it'll be better. The fish tend to eat the worms as they float up, thus ingesting the toxins.
Still, I would advise a fish to handle it for you. Take your time and look at your options, the fw aren't going anywhere and they won't do any harm.