some of my fish are scratching against plants etc, i know this usually means theres ich or something, but nothing appears to be wrong, theres no spots on any of them, and only a few of the fish are acting like this and it is usually one quick swipe , coul this be some microscopic parasite what soul i do a couple of weeks ago i had some ich, but the ich has been gone (medicated) and ive had several water changes since then any suggestions???