they are prtozoan worms from haveing a dirty tank.... they are harmless and will not go away.... u may think they have but unless you boil everythibng or pick up a uv sterilizer they are very very hard to get rid of.... ive tried copper salt raising the temp algea remover and some other things.... i got them when i started using liqued fry in 1 of my tanks.... if you dont feal like taking your tank down juss do lots of water changes and vacs scarpe the walls and you wont even notice them.... make sure you scarpe your walls clean this is where you will see them clinging near the top ..... uv wipes them out so you might cough the hundred dollers for 1 not a bad thing to have and a good reason to go get 1 good luck