Hook Worms?

I think my 7 year old tiger oscar has hook worms. Not sure though. A few months back I noticed what I thought were pieces of fuzz floating in the tank. When I took a closer look I discovered it was not fuzz but "worms". I even noticed that some were attached to him. My oscar has not changed feeding habit or his behavior. I'm not sure they even bother him at all. I've tried a few things the local pet stores have suggested but none have worked. When I do my water changes you can sometimes see the "worm" stuck to the sides of the tank. At times the "worms" are everywhere in the tank and other times you can't find them anywhere. Can't get any pictures that show them at all. Thank you for any information on how to get rid of these things.....I want Little Man to feel better.