So...what are these?

Yuck. I'd be inclined to remove that mass of hair algae and the worms along with it.
I imagine most fish would see them as a tasty snack however.
 
If you thing that's yuck you should have seen it a few weeks ago...
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Yeah, I hate worms. I'd freak out if I found that in my tank!
 
Well I have never had worms occur in any tank before this one.

So no one knows?

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Simple answer a worm. :D

But when you get down to things that size there are quite a number of things that are similar but have small differences. And even if you catch those differences you would only have a rough identification, since there are lots of individual species.
 
^ yup!

I figure if they are thriving with no fish in the tank, they're probably fish food instead of parasites.
 
Looking at how they're shaped and the way the body thins as they stretch, they look like a member of the tubifex family of worms; like the blackworms sold as fish food. If they are tubifex, they shouldn't pose a problem for fish.

Mark
 
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