Mits

In my opinion, yes. The ich does not really go away as long as there are hosts in your tank on which to feed. The stage of ich when the spots can be seen only lasts several days. When the spots are not visible, the ich is in a different stage of its lifecycle, normally in the rockwork somewhere when it dropped off the fish at night. After a period of time, those hatch and look for new hosts, which they must find in 24 hours or so or they die. Then the spots reappear. You can easily have multiple "waves" of ich in your tank that make it seem like the fish is always infected.

Many folks believe a strong fish can fight off ich. This is probably true. But since the ich is not really gone, another wave of the "spots" will eventually come and prey on the fish again. Over time, this will take it's toll on the fish. It should be mentioned that many folks have ich outbreaks in their reef tanks for long periods of time and they don't seem to lose fish. But I feel those people are in the minority... kind of like people that can grow SPS without protein skimmers... they exist, but you don't see it often.

I'm a big proponent of treatment... but you need to treat the tank, not necessarily the fish. You need to make sure the little buggers not currently on a fish are killed, so they don't reinfect other fish.

Other thoughts?

Ich has 4 life stages when it falls off it is in a the larva stages then moves to the free swimmer stage. by the time you see it on the fiish it is in the last stage. the parasite can live for 4 to 6 weeks with out a host in the right settings

Id try running a diatom filter in the tank for awhile it will take out the free floating ick parasites. It has been my understanding that the life cycle is around a month. Also ive read that hippos are more substitutable to ick then other fish. You would have to do this over a month to make sure you are picking it up as it becomes free floating.

i dont want to steer you in the wrong direction as we all know ick can be deadly but, IME the hippo tangs do not take well to tretment with copper. and hypo sounds easy but if your not on top of it, you will kill the fish with ammonia posion. if the fish has been seriving thus far than leave him be and feed him well to keep him healthy. keep the tank water at its best and siphon the gravel often. do what you can to keep stress low in the tank with high oxygin. drop the salinity to at least .022 if you have coral. if there are no coral in the tank than drop the salinity to .019 this only helps the fish breath and slows down the cycle of ick. if a hypo in a seperate tank is your choice of treatment, remember donot go lower than .009 and if you are keeping a filter or a piece of live rock in this tank, the bacteria will dye off once you lower salinity to around .015 good luck