Found little Red and Blue larvae looking critters

[PSCoral]

Found these in my tank while looking at it with a flash light , very small so it was hard to get a picture but if anyone would be able to tell me what they are or what they could be I’d appreciate it. I added what video and pictures I could take after catching two in sample cup

 

[papercrab]

they appear to be some kind of burrowing worm but then they move kinda like they are swimming so not a bristle worm or fire worm. They may be the swimmimg mate of a epitoke worm. If so they are harmless. Its hard to see from the videos but i would say they look harmless but best to get a second opinion.