Can anybody identify what these are?

[Gravityband]

Hey guys

My tank suffered from velvet and it killed all of my fish three months ago...I have been running my tank fish less for the past three months.. last night I noticed there are approximately five swimming crawling worms looking things in my tank. Can anybody identify what these are?!

 

[DSC reef]

Possibly dorvelleidae but need closer pics to identify.

 

[Gravityband]

Here is an enlarged pic.

 

[reef lover]

Dorvellidaes...harmless

 

[Gravityband]

Any comments on why this is happening tho? Too much nutrients? Water too dirty? Just trying to learn more about this situation...

 

[reef lover]

No fish to eat them probably.