Just because you cant se ick does not mean its gone. It love to hang out in the gills. keep doing what your doing but a few extra days will not hurt.
What are you using? I have treated ich more times then I would like to admit. Seems like almost every New fish I get has ich. A few of my LF are not the best when it comes to treating sick fish. Now when I get fish from these stores I know I will be dealing with it in a few days. I have even bought fish knowing they have ich to save them from the store.
Ich are like dog fleas. in fact I'm also dealing with ich. My new pleco Came from one of the bad stores has it. its so annoying even to treat in the small quarantine tank.