Do you have any live plants in the tank? If you do, it might just be infusoria which are totally harmless. There are all different kinds of "worms" that can be present in tanks. If you can tell us how they swim, how big they are, what color they are, and if they are effecting your fish, that would narrow it down quite a bit :p
hmmmm You could take out your fish and give your tank a HOT water rinse ( the plants, decorations, rocks, everything ) and that should get rid of any pests. No need for anything harsh like chemicals, unless you have a parasite which I doubt. :P **if you do have a live plant you might need to replace it depending if its infusoria. I once had a huge infusoria problem in my ten gal with all my live plants and hot water did the trick! :D Havnt spotted any since :P :/
Last edited by Larsa; 11-08-2011 at 10:52 AM.