sometimes they are just free floating in the water and not moving much, tilapia flakes would look more like ... flakes... if they are hair like then probably planarian. they don't just live in gravel, could live in sand too, basically any substrate or could even be in bare bottom tank.
once you remove their food source they will eventually die off but could take a while. other things you can do is add some cheap small fish into the tank like zebra danios, neon tetras, etc. they will eat those worms, hopefully they'll be able to clean them off before your rbps wipe them out.
keeping your water clean and remove all the uneaten food will def. in the long run.
even with sand you can vacuum out all the poop and uneaten food.
once you remove their food source they will eventually die off but could take a while. other things you can do is add some cheap small fish into the tank like zebra danios, neon tetras, etc. they will eat those worms, hopefully they'll be able to clean them off before your rbps wipe them out.
keeping your water clean and remove all the uneaten food will def. in the long run.
even with sand you can vacuum out all the poop and uneaten food.