Ich lives in the water and emerges as a killer when water quality or fish stress become an issue.
Actually, this is wrong. Ich only lives for around 7 days depending on the temperature. In order to reproduce the next generation it NEEDS to infect fish. However, it can be brought in on live plants, snails, etc and decor that has been in an infected tank and when there is only a small amount in the tank it can go unnoticed until the infection spreads. This is how the myth that it "lies in wait" started (and have been propagated by Petco and other big box stores to try to offload the liability of buying sick fish from them). Certainly stressed fish are more susceptible to getting sicker faster or being the first fish to show signs of ich.
Bottom line, the only way your tank has ich is if you have brought it in on something else within the last week or so. Established tanks that have had nothing added (nor nets etc used from a tank that has had additions) cannot just spontaneously develop ich.
