Here's the part that puzzles me: Let's say that there is some percentage of Ich parasites that can remain in a dormant state for weeks, months, years, whatever. In that state, they are non-infective; they must be released from the cysts, at which point they are free-swimming and must find hosts within a short time. That's the stage of the life cycle which we can kill; when they're encysted, or later when they are embedded in the host, they are pretty much untouchable. We need to kill that vulnerable free-swimming stage. This is why treatments must continue for at least a couple weeks, so that any parasites that are in another stage of the life-cycle eventually become vulnerable to treatments.
Now the "common wisdom" that I mentioned earlier always preached that an infestation of Ich results from stressing the fish, often by a sudden drop in water temperature; just from experience, this seemed to be believable. Okay, so...the fish are stressed and susceptible...but what caused the encysted, dormant parasites to become released and free-swimming, and thus infective? Merely stressing the fish doesn't make the encysted parasites able to latch onto them; they must escape their cysts first. How, when and why do they do that? What makes a dormant parasite suddenly re-animate and go on the hunt for a host...at just the exact time that the host is stressed and susceptible? Does that same temperature drop "wake them up"?
Or, is the parasite virulent enough in the infective free-swimming stage that it's going to infect any fish, stressed or not? If that's the case, we're back to that same question, i.e. what caused them to break out of their cysts?
If there is simply some random time at which the cysts break open...why then do some tanks never get an Ich infestation? I've dealt with Ich many times over the years...it's more of an inconvenience than a deadly threat...but I've also had tanks that have run for years...in one case for almost 15 years...and never had a white spot during that entire time? Just luck of the draw? Or is Ich not that universally distributed amongst all water bodies and fishtanks, as we are often told?
Too many questions; I hope the OP is about to answer all of them!
