Ich is a weird parasite. Sometimes fish can be infected with it at very low levels for long periods of time and never show any adverse effects. It is often present to some extent in all aquariums, and is opportunistic in that it infects your fish when their immune systems are weakened from some sort of stress (e.g. shipping, handling, changing tanks, malnutrition, aggression from other fish, etc.). Treating it sooner rather than later is usually a good idea, because if it gets out of control it can down your whole system. You'd have to remove any invertebrates from your tank before you treat, since most inverts are extremely sensitive to copper-based medications and will die from them. The Ich might go away on its own, but IMO, you're better off treating for it.