This happened in my last tank too but not this clearly bad. Ive only had the tank less than a month, its fully cycled for the last week or so. It has one betta , couple plants. I dont overfeed, i give her about 3 pellets or a couple bloodworms twice a day and make sure she eats it all so theres no excess waste. is that overfeeding? I did a water change today and theyre still floating all around the water column. The fish is unbothered by them but unfortunately wont eat them, theyre too small for her. im just double checking theyre harmless nemotodes or something and if i keep doing water changes of 50% twice a week or so they wont get any more infested? idk what to do if they keep breeding:'( Oh and i had a strong light on the tank before which i thought mightve made it worse? i switched to a less powerful one now.