Dont have Ick, Dont want Ick

[alarmguy66]

Simple question. Is the ONLY way for Ick to be introduced to a tank through the addition of a fish (not invert or rock) carrying it?

 

[fishfreek]

Some say the parasite that causes ich is always in the tank and only when fish are stressed to a point where their natural imune system is not able to fend off the parasite do we see the results of an ich infestation.