I've successfully managed ich on a Yellowtail Angel twice without using either hyposalinity or copper. The first time was in Q - during a post acquisition outbreak. For several reasons my Q tank has some inverts in it (zoos, shrooms) - which effectively makes it a "mini" reef. I first treated by adding metronidazole to the water, but after several weeks the infection just got cyclically worse. I than switched to a medicated feed (metronidazole @ 250 mg/100 g (of food = fresh clams, mussels and frozen squid and supplemental vitamins), which was fed 2x per day, I added two cleaner shrimp, and put a UV filter in. Can't say what exactly what worked, but the infection cleared up relatively quickly, but believe that the shrimp played a big (probably biggest) role. The Yellowtail was "spot free" for about 6 weeks and then moved into my main display. Shortly thereafter my Regal Angel terrorised it and I started to notice white spots on it! The aggression was very persistent and I considered tearing my tank apart to get the fish out as I was worried about the health of the Yellowtail, but also that the Regal Angel and the others (including a Regal Tang) might come down hard with ich. However, as I had the medicated feed on hand I started up with it (1x/day) and added a second cleaner shrimp to the tank (one was already in there); but no UV. Again, not sure what worked but the fish slowly cleared up and has been fine ever since (well over a month now). It is also important to note that the aggression from the Regal Angel had abated considerably.
A long time prior to that when I got the Regal Tang, which was a tiny thing not more than 1.5" long, I noticed a couple of white spots, which I was reasonably certain were ich. There wasn't much I could do so I waited it out, focusing on water quality and nutrition (including the use of some supplemental vitamins) and the infection never developed into clinical disease. At the time there was one cleaner shrimp in the tank. I never saw Crypt in the tank until many months later during the Yellowtail incident.
So I guess only two of these incidences qualify as leaving the tank "alone" as the use of metro in the feed on the latter two incidences is next to impossible to assess/interpret. However, they all suggest to me that you can live with ich. I would only consider drastic treatment measures (= tearing you tank down to get the fish out and treating hypo or copper) if the infection became very severe and it was clear the fish would be lost if I didn't intervene.
I think VSpeck makes a very salient point about stress and the incidence and management of ich. If you reduce stress as much as possible, there is a good chance, IMO/E, that fish can fight it off via natural immunity. Without a doubt, the sit back and wait approach is very risky, and to a large extent dependent on the pathogenicity of the particular strain of Cryp you're dealing with and the physiological state of your fish (vis a vis stess). The issue of acquired immunity was discussed in a previous thread which you might be interesting in having a look at (
http://www.reefcentral.com/forums/showthread.php?s=&threadid=700083).
