No one mentioned this, but ich infects your whole tank, not just single fish. If you are using a salt/heat treatment that will clear it up, but I believe actually seeing ich particles on the outside of the body of the fish is one of the last signs. I think it can hide out in the gills where you wouldn't see it for quite a while, until it spreads to the outer body. This is why it is supposedly recurrent in tanks, it is never cleared up completely to begin with and is just not visible. FYI
, so you can treat effectively