Weird Worm Things?

[Danio8]

After doing a 90% water change yesterday, I noticed these tiny white things. I did another 50% water change today and after refilling the tank, I noticed them floating around again. I think they are worms because some of them seem to squirm around. I haven’t noticed them crawling around anywhere, just floating and occasionally squirming in the water. They are about 1 mm long.

[Danio8]

Oh and the tank used to belong to a betta with fin rot who recently died. I never noticed any worms on him. I also added brand new driftwood that was boiled for 1 hour today. There were also new rocks added today that were very dusty. I rinsed the rocks off and soaked them in a bowl of water. I did not notice any of the worm things while soaking the rocks.

[Danio8]

Ok so I caught one in a glass and have been watching it for a few minutes and it has not seemed to move. I think they may just be plant fibers.

[Colin_T]

Probably detritus worms. They normally live in the substrate and only come out if the gravel gets too dirty or there is something in the water they don't like. Then you see them on the glass or wiggling through the water. They are harmless and occur in every freshwater aquarium. They probably popped up because you did a big water change and that upset them.