I think my fish has some sort of worm?

If it is a fish only tank that has no invertebrates that would be harmed by parasite tablets then I would de worm the tank and the fish then perform 3 50% water changes using all de-chlorinated water and be sure the PH and temperature are the same before changing as a big change in temp in short time can kill fish and a small change in PH can be enough to cause stress on the fish that can cause problems later. For instance, stress makes fish susceptible to parasites. Draining the whole tank and cleaning it should not be an option at all. Worms happen and parasites happen. If draining and cleaning a tank was the way to handle these problems then most aquariums would be impossable to maintain. Such as a reef tank, mine has more types of worm in it than i can identify. 10 gallon quarentene tanks are the absolute best option when dealing with a serious aquarium. If you do have invertabrates in your tank and want to safely use a wormer you will have to remove them and worm the tank. Then remove the fish and fully drain for a 100% water change. Re-acclimate your livestock back into the fresh tank.

If I were you. I'd take one of the worms to petco to see what it is. They can/do run test. Just changing the aquarium is not enough. They will come back most likely. It could be in your fish now... The worms need to be killed.