My tank had an outbreak (not severe, but a visible number) of tiny, threadlike worms called nematodes. At least, I think
I hate worms.
But I hate them a little less now.
I was and still am squirmish at the thought of those worms flicking around in the tank, but was delighted to see my betta Darcy hang around the sponge filter and pick at them. I think the worms are a good protein source for him. I hope he does some population control so the worm problem doesn't get out of hand.