Tiny white worms (Planaria) How do i get rid of them???

I have never had white worms in my tank. I know white worms are in ponds and it is caused from bird poo, but in this case I wouldn't know what to tell you. I would see if the pet shop has any chemicals to help cure this problem. Goldfish carry alto of bacteria, so we started giving our pirania minos. If you are able to put the fish in a different tank and do a complete water change I would do that. We have even used a 10 gallon bucket, but we use chemicals and check our water before putting our fish back in.