Not sure if this is the right place for it, but...
My dad has a tank (about 20 gal. I believe) in his office that's filled with guppies and platies and their bazillion offspring.
It's...pretty dirty. The gravel is, at least. The tank is planted with a huge amazon sword and something else i'm not sure of, but the bottom has a lot of gunk and uneaten food.
Anyway, the point is, I've noticed my dad's tank has these weird...worm things...in the gravel. They pop out when the fish are being fed.
They're pretty big actually, for worms, the biggest I saw was about 2 inches or so.
They look kinda like...fish poo tbh. Same colour anyway, and they're long and more on the thin side.
I don't think they attack or harm the fish, not that I've seen. The fish will occasionally bite them and they'll retreat to the gravel, but I haven't seen the worms harming the fish physically.
Still, they're really gross and i'd like to know what they are and if we can get rid of them.