White worms in tank? (Repost)

[KFav93]

Okay, I'm reposting this because I didn't get a clear answer. I have these little white worms in my tank, sometimes they stick to fish, but they fall off right away and when I do a water change and stir up the water they float around. They do not stick to the glass. A lot of the times I see them in the gravel. I vacuumed again today trying to get rid of more. What are these from and how can I get rid of them? They are very thin and small I would compare it to thin spaghetti noodles. I feed my fish pellets. I looked up planaria and hydra and the worms don't look like those.
My stock includes:
4 zebra danios
5 platys
1 catfish
1 zebra snail

Also, it's a 20 gallon tank.