When you see ich (white spots), its already ruptured or close to it and now in the tank by the thousands or about to be. The white spots are basically 'pregnant' or ruptured ich. You cannot see ich when it is burrowed in the fishes skin and feeding. Seeing no white spots means absolutely nothing.
So...quite often people see the white spots come and then go within a few days and think ich is gone or 'better'. By this time, your fish can be absolutely covered in ich but you won't see it.
What I am getting at is that you only know your 'ahead' of the ich once you don't see many white spots for a long time. I find that if you keep the fish stress free and don't add new fish to its tank for a few months, the number of white spots you see will lessen and lessen to a manageable number. Just watch for stress like rubbing or heavy breathing. That's when you need to start treating as they can go downhill very fast at this point. But as long as he is acting fine and eating, let him fight it off. If I were lucky enough to get an Achilles tang happy and even thriving in my tank, I would probably never add new tankmates. Even with my hippo, new fish to the tank mean a month or two of severe ich for him
Seems like he is doing ok though
